WO2013146317A1 - Silicon-based electro-optical device - Google Patents

Silicon-based electro-optical device Download PDF

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Publication number
WO2013146317A1
WO2013146317A1 PCT/JP2013/057270 JP2013057270W WO2013146317A1 WO 2013146317 A1 WO2013146317 A1 WO 2013146317A1 JP 2013057270 W JP2013057270 W JP 2013057270W WO 2013146317 A1 WO2013146317 A1 WO 2013146317A1
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silicon
optical device
optical
layer
based electro
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PCT/JP2013/057270
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French (fr)
Japanese (ja)
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藤方　潤一
重樹 高橋
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日本電気株式会社
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Priority to US14/388,249 priority Critical patent/US9341868B2/en
Priority to JP2014507675A priority patent/JP6187456B2/en
Publication of WO2013146317A1 publication Critical patent/WO2013146317A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction
    • G02F1/025—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G02F1/2257—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure the optical waveguides being made of semiconducting material
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction
    • G02F1/0151—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction modulating the refractive index
    • G02F1/0152—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction modulating the refractive index using free carrier effects, e.g. plasma effect
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/212—Mach-Zehnder type
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/10—Materials and properties semiconductor
    • G02F2202/104—Materials and properties semiconductor poly-Si

Definitions

  • the present invention relates to a silicon-based electro-optical device that converts a high-speed electrical signal into an optical signal at high speed, which is necessary in the information processing and communication fields.
  • the present invention relates to a silicon-based electro-optical device using a silicon-insulator-silicon capacitor structure formed on an on-insulator (SOI) substrate.
  • SOI on-insulator
  • CMOS complementary metal oxide semiconductor
  • optical modulators and optical switches that change the refractive index using the thermo-optic effect of silicon are slow and can only be used at device speeds up to a modulation frequency of 1 Mbps. Therefore, in order to realize a high modulation frequency required for more optical communication systems, an optical modulator or an optical switch using an electro-optical effect that enables high-speed operation is required.
  • a phase difference is given to one or both of the lights propagating through the two arms due to the refractive index change, and these lights are made to interfere with each other, thereby obtaining an intensity modulation signal of the light. It is done.
  • the free carrier density in the electro-optic modulator can be changed by free carrier injection, accumulation, removal, or inversion.
  • many of the electro-optic modulators that have already been studied have poor optical modulation efficiency, and the length necessary for optical phase modulation (hereinafter simply referred to as “optical phase modulation length”) is on the order of 1 mm, An injection current density higher than cm 3 is required. If the optical phase modulation length of the electro-optic modulator is long and the element size is large, it becomes more susceptible to the temperature distribution on the silicon platform, and the original electro-optic due to the refractive index change of the silicon layer due to the thermo-optic effect. The effect may be countered. Therefore, in order to realize a small size, high integration, and low power consumption of the electro-optic modulator, an element structure capable of obtaining high light modulation efficiency is required.
  • Non-Patent Document 1 discloses a silicon-based electro-optic device having a rib waveguide structure on an SOI substrate.
  • slab regions extending laterally on both sides of a rib waveguide structure made of an intrinsic semiconductor region are doped in p-type and n-type, respectively.
  • the rib waveguide structure is formed using a silicon layer 1S on an SOI substrate including a support substrate 3 made of silicon and a buried oxide layer 2.
  • the rib waveguide structure is a PIN diode type modulator that changes the free carrier density in the intrinsic semiconductor region by applying forward and reverse biases, and uses the carrier plasma effect to change the refractive index. It has a changing structure.
  • intrinsic semiconductor silicon 1 is formed so as to include p + doped semiconductor silicon 4 formed by highly doping silicon layer 1S in contact with first electrode contact layer 6A. Yes.
  • intrinsic semiconductor silicon 1 includes n + doped semiconductor silicon 5 that is highly doped with respect to silicon layer 1S, and second electrode contact layer 6B connected thereto.
  • the p + and n + doped semiconductor silicon 4, 5 is doped to exhibit a carrier density of about 10 20 per cm 3 .
  • the first and second electrode contact layers 6 ⁇ / b> A and 6 ⁇ / b> B are connected to a power source (not shown) through the electrode wiring 7.
  • a forward bias to the PIN diode using the first and second electrode contact layers 6A and 6B, free carriers are injected into the waveguide.
  • the refractive index of the intrinsic semiconductor silicon 1 changes, whereby phase modulation of light propagating in the waveguide is performed.
  • Patent Document 1 discloses a silicon-based electro-optic device having a SIS (silicon-insulator-silicon) type structure formed on an SOI platform.
  • a silicon-based electro-optical device described in Patent Document 1 includes an n-doped polycrystalline silicon 10 that is a main body region formed on a relatively thin silicon surface layer of an SOI substrate, and an n-doped polycrystalline silicon. 10 is made of p-doped semiconductor silicon 9 which is a gate region laminated so as to partially overlap with 10. A relatively thin dielectric layer 12 is formed at the laminated interface between the p-doped semiconductor silicon 9 and the n-doped polycrystalline silicon 10.
  • the carrier density change is controlled by the external signal voltage via the electrode wiring 7 and the p + and n + doped semiconductor silicon 4 and 11. It is stipulated that
  • Non-Patent Document 1 The operating speed of the silicon-based electro-optical device described in Non-Patent Document 1 is limited by the free carrier lifetime in intrinsic semiconductor silicon 1 and carrier diffusion when the forward bias is removed. Thus, related art PIN diode modulators typically have operating speeds in the range of 10-50 Mbps during forward bias operation. On the other hand, in order to shorten the carrier life, it is possible to increase the switching speed by introducing impurities into the intrinsic semiconductor silicon 1, but the introduced impurities reduce the light modulation efficiency. . The largest factor that affects the operating speed of the PIN diode type modulator is the RC time constant. In the case of the rib waveguide structure, the electrostatic capacity (C) when a forward bias is applied is equal to that of the PN junction.
  • C electrostatic capacity
  • optical phase modulation is performed by accumulating, removing, or inverting free carriers on both sides of the dielectric layer 12.
  • the region where the carrier density changes dynamically becomes as thin as about several tens of nanometers. For this reason, an optical phase modulation length on the order of mm is required. As a result, there is a problem that the silicon-based electro-optical device becomes large and high-speed operation becomes difficult.
  • the present invention solves the above-described problems, and achieves low current density, low power consumption, high modulation degree, low voltage drive, and high-speed modulation in a submicron in a silicon-based electro-optical device that can be integrated on a silicon substrate.
  • An object of the present invention is to provide a silicon-based electro-optical device capable of realizing an optical modulator structure based on the carrier plasma effect, which can be realized in a region, at a low cost.
  • the silicon-based electro-optical device is formed by laminating at least a part of a silicon semiconductor layer doped to exhibit the first conductivity type and a silicon semiconductor layer doped to exhibit the second conductivity type.
  • the silicon-based electro-optical device of the present invention light modulation based on the carrier plasma effect that can realize low current density, low power consumption, high modulation degree, low voltage drive, and high-speed modulation in the submicron region.
  • the vessel structure can be realized at low cost.
  • FIG. 1 is a cross-sectional view of a silicon-based electro-optical device according to a first embodiment of the invention.
  • 1 is a plan view of a silicon-based electro-optical device according to a first embodiment of the present invention, and is a plan view in a light propagation direction.
  • FIG. FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a second embodiment of the invention.
  • FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a third embodiment of the invention.
  • FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a fourth embodiment of the invention.
  • FIG. 10 is a cross-sectional view of a silicon-based electro-optical device according to a fifth embodiment of the invention.
  • FIG. 10 is a plan view of a silicon-based electro-optical device according to a fifth embodiment of the invention, and is a plan view in the light propagation direction. It is sectional drawing which shows the manufacturing process of the silicon base electro-optical apparatus which concerns on 1st Embodiment of this invention. It is a top view for demonstrating the structure of the Mach-Zehnder interferometer type
  • FIG. 1 is a cross-sectional view of a silicon-based electro-optical device disclosed in Non-Patent Document 1.
  • FIG. 1 is a cross-sectional view of a silicon-based electro-optical device disclosed in Patent Document 1.
  • the silicon-based electro-optical device according to the embodiment of the present invention shown in FIGS. 1 to 13 utilizes an electro-optical effect (free carrier plasma effect).
  • the outline of the optical phase modulation mechanism in silicon which is the principle of operation in the silicon-based electro-optical device of the present invention, will be described below.
  • ⁇ n and ⁇ k represent the real part and the imaginary part of the refractive index change of the silicon semiconductor layer
  • e is the charge
  • ⁇ is the wavelength of light
  • ⁇ 0 is the dielectric in vacuum
  • N is the refractive index of intrinsic semiconductor silicon
  • m e is the effective mass of the electron carrier
  • m h is the effective mass of the hole carrier
  • ⁇ e is the mobility of the electron carrier
  • ⁇ h is the mobility of the hole carrier
  • ⁇ N e is The electron carrier concentration change
  • ⁇ N h is the hole carrier concentration change.
  • the Si 1-x Ge x layer has a higher refractive index than the silicon semiconductor layer, there is an effect of improving the overlap between the region where the free carrier density changes and the optical field. Furthermore, the length of the active layer can be remarkably reduced by making the Si 1-x Ge x layer uneven as described above.
  • the free carrier plasma effect is further enhanced by increasing the Ge composition in the Si 1-x Ge x layer.
  • L in Equation (3) is the length of the active layer along the light propagation direction of the silicon-based electro-optical device.
  • the amount of phase change is exerted as a great effect as compared with light absorption.
  • the silicon-based electro-optical device described below can basically exhibit characteristics as a phase modulator.
  • FIG. 1 shows a cross-sectional view of an electro-optic phase modulator (silicon-based electro-optic device) 101 according to the first embodiment to which the present invention is applied.
  • Electro-optic phase modulator 101 Si 1-x Ge x consisting layer irregularities (hereinafter, simply referred to as "Si 1-x Ge x uneven layer") 13, a relatively thin dielectric layer (dielectric) 12 and N-doped polycrystalline silicon (silicon semiconductor layer exhibiting the second conductivity type) 10.
  • the electro-optic phase modulator 101 is formed on an SOI substrate in which a support substrate 3, a buried oxide layer 2, and p-doped polycrystalline silicon (a silicon semiconductor layer exhibiting the first conductivity type) 9 are sequentially stacked. Yes.
  • a portion of the n-doped polycrystalline silicon 10 that is in contact with the dielectric layer 12 is illustrated as an n-doped polycrystalline silicon 19.
  • the present invention is characterized in that the relatively thin dielectric layer 12 is composed of at least one layer of silicon oxide, silicon nitride, hafnium oxide, zirconium oxide, and aluminum oxide. Further, the relatively thin dielectric layer 12 has a thickness of 0.1 nm to 50 nm.
  • the relatively thin dielectric increases the dielectric constant and reduces the film thickness when free carriers are accumulated on both sides of the dielectric layer 12, thereby improving the modulation efficiency. It will be improved.
  • an increase in electric capacity decreases the frequency band during high-speed operation, and therefore an optimum film thickness and material are applied to achieve the target modulation efficiency and high speed.
  • the film thickness if it is thinner than 0.1 nm, there is a practical problem of leakage current, and if it is thicker than 50 nm, the modulation efficiency is greatly reduced. Therefore, it is preferable to design in the range of 0.1 nm to 50 nm.
  • the Si 1-x Ge x concavo-convex layer 13 is provided on the surface of the p-doped semiconductor silicon 9 of the SOI substrate.
  • the relatively thin dielectric layer 12 is formed on a part of the surface of the Si 1-x Ge x uneven layer 13 and the SOI layer. Therefore, not only the uppermost surface of the Si 1-x Ge x concavo-convex layer 13 but all exposed surfaces of the side surfaces and the depressions are covered with the dielectric layer 12.
  • the n-doped polycrystalline silicon 10 is laminated so as to cover the surface irregularities on the dielectric layer 12. In order to reduce optical loss, the surface of the n-doped polycrystalline silicon 10 may be smoothed by polishing.
  • An electrode wiring 7 for applying a driving voltage from the outside is connected to each of the p and n doped polycrystalline silicons 9 and 10. Further, p + and n + doped semiconductor silicons 4 and 11 subjected to high concentration doping are formed at connection portions between the p and n doped polycrystalline silicons 9 and 10 and the electrode wiring 7.
  • the p + and n + doped semiconductor silicons 4 and 11 function as contacts of the electrode wiring 7, but the contact layers 6 are respectively provided at the interfaces between the p + and n + doped semiconductor silicon 4 and 11 and the electrode wiring 7 as necessary. It may be provided.
  • the p- and n-doped polycrystalline silicons 9 and 10 are composed of at least one layer selected from the group consisting of polycrystalline silicon, amorphous silicon, strained silicon, single crystal silicon, and Si 1-x Ge x .
  • the electro-optic phase modulator 101 by providing the Si 1-x Ge x uneven layer 13 at the SIS junction interface, the overlap between the optical field and the carrier density modulation region is increased. Further, by adopting the Si 1-x Ge x layer 13, a larger carrier plasma effect than that of the silicon semiconductor layer can be obtained, so that the size of the electro-optic phase modulator 101 can be reduced. Further, by further increasing the doping density of the p and n doped polycrystalline silicon 9 and 10 adjacent to the SIS junction interface, the series resistance component can be reduced and the RC time constant can be reduced.
  • the electro-optic phase modulator 101 in order to reduce the light absorption loss due to the overlap between the region where the doping density of the p and n doped polycrystalline silicon 9 and 10 is increased and the optical field, Is a waveguide having a rib / ridge shape as shown in FIG.
  • an electro-optic phase modulator capable of operating at high speed with small optical loss and RC time constant can be realized.
  • the unevenness provided at the SIS junction interface is formed by forming the Si 1-x Ge x uneven layer 13 on the surface of the p-doped semiconductor silicon 9, the dielectric layer 12, and the n-doped polycrystalline silicon 10 on the dielectric layer 12. This is realized by stacking the layers.
  • the unevenness interval (period) in the Si 1-x Ge x uneven layer 13 is equal to the thickness (hereinafter referred to as the maximum depletion layer thickness) W of the semiconductor layer in which free carriers are accumulated, removed, or inverted on both sides of the dielectric layer 12.
  • W the thickness
  • it is preferably 2 W or less.
  • the maximum depletion layer thickness W in the thermal equilibrium state is given by the following equation (4).
  • Equation (4) ⁇ s is the dielectric constant of the semiconductor layer, k is the Boltzmann constant, N c is the carrier density, ni is the intrinsic carrier concentration, and e is the charge amount.
  • N c 10 17 / cm 3
  • the maximum depletion layer thickness is about 0.1 ⁇ m, and as the carrier density increases, the depletion layer thickness, that is, the thickness of the region where the carrier density modulation occurs is thin.
  • the height of the unevenness in the Si 1-x Ge x uneven layer 13 is determined when the effective refractive index acting on the optical signal electric field in the electro-optic phase modulator 101 is n eff and the wavelength of the optical signal is ⁇ . , ⁇ / n eff or less is preferable.
  • FIG. 2 is a plan view of the electro-optic phase modulator 101 shown in FIG. 1 in the light propagation direction (Z direction shown in FIG. 1).
  • accumulation of carriers, depletion, or inversion occurs on both sides of a relatively thin dielectric layer when an electric signal is applied as a driving voltage.
  • the thickness of the region where the carrier density is modulated is estimated to be 100 nm or less. Therefore, the region where the carrier density is modulated with respect to the spread of the optical signal electric field is very small, and the modulation efficiency is generally poor.
  • the region where the carrier density is modulated is the uneven region formed of the Si 1-x Ge x layer 13 having the SIS junction shape provided on the surface of the p-doped semiconductor silicon 9.
  • the region where the carrier density is modulated is the uneven region formed of the Si 1-x Ge x layer 13 having the SIS junction shape provided on the surface of the p-doped semiconductor silicon 9.
  • FIG. 3 shows a cross-sectional view of an electro-optic phase modulator 102 according to a second embodiment to which the present invention is applied.
  • the same components as those of the electro-optic phase modulator 101 of the first embodiment are denoted by the same reference numerals, and the description thereof will be given. Is omitted.
  • the surface of the p-doped semiconductor silicon 9 of the SOI substrate has two or more kinds of Si 1-x Ge x compositions in the direction orthogonal to the light transmission direction. Concavities and convexities made of the laminated structure 14 are formed.
  • FIG. 3 illustrates a laminated structure 14 including two types of Si 1-x Ge x uneven layers 14a and 14b having different Ge compositions x.
  • the stacked structure 14 of two or more types of Si 1-x Ge x concavo-convex layers having different Ge compositions By providing the stacked structure 14 of two or more types of Si 1-x Ge x concavo-convex layers having different Ge compositions, crystal defects when the Ge composition is increased are reduced, and the dielectric layer 12 It becomes possible to realize a layer structure in which the carrier plasma effect near the interface is further enhanced.
  • FIG. 4 shows a cross-sectional view of an electro-optic phase modulator 103 according to a third embodiment to which the present invention is applied.
  • a Si 1-x Ge x concavo-convex layer 15 whose composition is modulated in the film thickness direction is formed on the surface of the SOI layer.
  • crystal defects are increased when the Ge composition x is increased, and the carrier plasma effect near the interface with the dielectric layer 12 is further improved. It is possible to realize a layer structure.
  • FIG. 5 shows a cross-sectional view of an electro-optic phase modulator 104 according to a fourth embodiment to which the present invention is applied.
  • the unevenness of the Si 1-x Ge x uneven layer 16 on the surface of the SOI layer is relative to the propagation direction of the optical signal (Z direction shown in FIG. 5).
  • Z direction shown in FIG. 5 the propagation direction of the optical signal
  • X direction shown in FIG. 5 the vertical direction
  • FIG. 6 shows a cross-sectional view of an electro-optic phase modulator 105 according to a fifth embodiment to which the present invention is applied.
  • the unevenness of the Si 1-x Ge x uneven layer 17 on the surface of the SOI layer is parallel to the propagation direction of the optical signal (see FIG. 6). (Z direction shown).
  • FIG. 7 is a plan view of the electro-optic phase modulator 105 in the light propagation direction.
  • the interval between the uneven shapes on the surface is preferably 2 W or less.
  • the unevenness of the Si 1-x Ge x uneven layer 17 may be periodically formed so as to reduce the group velocity of the optical signal.
  • the effective refractive index acting on the optical signal electric field is n eff and the optical signal wavelength is ⁇
  • it is aperiodic so as to have an interval of ⁇ / n eff or less. May be formed.
  • FIG. 8A is a cross-sectional view of an SOI substrate for forming an electro-optic phase modulator.
  • the SOI substrate has a structure in which a p-type doped polycrystalline silicon 9 of about 100 to 1000 nm is laminated on the buried oxide layer 2 on the support substrate 3.
  • a structure having a buried oxide layer thickness of 1000 nm or more In order to reduce optical loss, it is preferable to use a structure having a buried oxide layer thickness of 1000 nm or more.
  • the p-type doped polycrystalline silicon 9 on the buried oxide layer 2 is a p-type dopant by using a substrate previously doped so as to exhibit the first conductivity type (p-type) or by ion implantation or the like. Heat treatment may be performed after the surface layer is doped with P or B.
  • an oxide film mask 18 for forming irregularities made of a Si 1-x Ge x layer is formed on the p-type doped polycrystalline silicon 9 by a low pressure CVD method or the like. Form by the method. Thereafter, an opening pattern having a width of, for example, about 200 nm is formed in the light modulation portion by photolithography or electron beam lithography. Thereafter, the Si 1-x Ge x uneven layer 13 having a height of, for example, about 50 to 100 nm is selectively grown on the opening pattern by an ultrahigh vacuum CVD method or a low pressure CVD method.
  • the hard mask layer 20 is patterned by photolithography or electron beam lithography. Further, by using the formed pattern, the non-doped polycrystalline silicon 19n is formed into a rib-type waveguide shape by a reactive plasma etching method or the like so that the width of the optical waveguide structure is 0.3 ⁇ m or more and 2 ⁇ m or less in the light modulation portion. Process.
  • a p + doped semiconductor silicon 4 is formed on the p-type doped polycrystalline silicon 9 which is an SOI layer by ion implantation.
  • an oxide film clad layer 8 is formed by a film forming method such as a plasma CVD method, and planarized by CMP.
  • a polycrystalline silicon layer serving as an upper electrode extraction layer is stacked, and n-type conductivity is exhibited together with non-doped polycrystalline silicon 19n by n-type ion implantation. Dope treatment. Further, the non-doped polycrystalline silicon 19n may be doped during film formation so as to exhibit the n type.
  • an n + doped polycrystalline silicon 11 is formed in the upper electrode lead layer of the n doped polycrystalline silicon 10 by ion implantation.
  • the oxide film cladding layer 8 is stacked by plasma CVD or the like, and after forming the contact hole 21 by reactive etching, p + doped semiconductor silicon 4 and n + doped polycrystalline silicon 11 are formed.
  • An electrode contact layer 6 is formed on each surface.
  • the electrode contact layer 6 may be formed of a silicide layer or the like by laminating a metal such as Ni on the semiconductor silicon layer and annealing it.
  • a metal layer such as Ti / TiN / Al (Cu) or Ti / TiN / W is formed to fill the contact hole 21 by sputtering or CVD, and the reaction
  • the electrode wiring 7 is formed by patterning by reactive etching. Formation of the electrode wiring 7 enables connection with the drive circuit.
  • FIG. 9 is a configuration diagram of an MZM type optical intensity modulator (Mach-Zehnder interferometer type structure) 206 according to the sixth embodiment to which the present invention is applied.
  • the MZM type light intensity modulator 206 includes a first arm 22 and a second arm 23 in which the electro-optic phase modulators of any of the first to fifth embodiments are arranged in parallel.
  • An optical branching structure 25 that branches light on the input side of the first and second arms 22 and 23 and an optical coupling structure 26 that couples on the output side are connected.
  • the phase modulation of the optical signal is performed by the first and second arms 22 and 23, and then phase interference is performed by the optical coupling structure 26, whereby the input light is modulated by the light intensity. Converted to a signal.
  • the input light is branched so as to have the same power as that of the first and second arms 22 and 23 by the light branching structure 25 arranged on the input side.
  • the carrier accumulation mode the refractive index acting on the optical signal electric field in the electro-optical device is reduced, and in the carrier removal (depletion) mode, the refractive index acting on the optical signal electric field is increased, and the light in both arms The signal phase difference is maximized.
  • Optical intensity modulation occurs by combining the optical signals transmitted through both arms by the optical coupling structure on the output side.
  • the MZM type light intensity modulator 206 having the above-described configuration, it is possible to modulate the light intensity of the input light with low current density, low power consumption, high modulation degree, low voltage drive, and high speed modulation.
  • FIG. 10 is a configuration diagram of an MZM type light intensity modulator 207 according to the seventh embodiment to which the present invention is applied.
  • the MZM light intensity modulator 207 has a configuration in which the MZM light intensity modulators 206 are arranged in parallel. With the above configuration, the same effect as that of the MZM type light intensity modulator 206 can be obtained, and parallel processing in the light intensity modulation of input light can be performed.
  • FIG. 11 is a configuration diagram of an MZM type light intensity modulator 208 according to the eighth embodiment to which the present invention is applied.
  • the MZM light intensity modulator 208 has a configuration in which a plurality of MZM light intensity modulators 206 or MZM light intensity modulators 207 are arranged in series.
  • the MZM type optical intensity modulators 207 and 208 can be applied to an optical modulator having a higher transfer rate, a matrix optical switch, or the like.
  • Example 1 The electro-optic phase modulator 101 according to the first embodiment is manufactured by the steps shown in FIGS.
  • the wavelength ⁇ of the input light was set to 1550 nm, the wavelength was taken into consideration, and other conditions were set as.
  • the thickness W of the semiconductor layer in which free carriers are accumulated, removed, or inverted on both sides of the dielectric layer 12 is set to 160 nm, and the unevenness interval of the Si 1-x Ge x uneven layer 13 is approximately 160 nm, which is the same as W. It was as follows.
  • Example 1 An electro-optic phase modulator was manufactured under the same conditions as in Example 1 except that the Si 1-x Ge x uneven layer 13 was not provided with unevenness.
  • FIG. 12 shows the dependence of the phase shift amount on the length of the optical signal propagation direction in the electro-optic phase modulator fabricated in Example 1 and Comparative Example 1. It was confirmed that the light modulation efficiency in the electro-optic phase modulator of Example 1 was remarkably improved by forming irregularities with an interval of about 160 nm or less, which is the same as the thickness W of carrier modulation. It was confirmed that the light modulation efficiency was improved by increasing the depth of the unevenness of the Si 1-x Ge x uneven layer 13.
  • FIG. 13 shows the carrier density dependence of the operating frequency band in the electro-optic phase modulator manufactured in Example 1 and Comparative Example 1.
  • the operating frequency band of optical phase modulation has a trade-off between the effect of reducing the size by improving the modulation efficiency and the effect of increasing the electric capacity by providing the unevenness.
  • the effective refractive index acting on the optical signal electric field is n eff and the optical signal wavelength is ⁇
  • the frequency band becomes wide when the depth of the unevenness is ⁇ / n eff or less. It was confirmed that a high-speed operation of 10 GHz or more is possible by setting the carrier density to about 10 18 / cm 3 .
  • the carrier mobility in the polycrystalline silicon layer is a problem in high-speed operation. Therefore, increase the particle size by recrystallization by annealing treatment, improve carrier mobility, or improve the crystal quality of the n-doped polycrystalline silicon 10 by using an epitaxial lateral growth (ELO) method or the like. Is effective.
  • ELO epitaxial lateral growth
  • Example 2 Using the electro-optic phase modulator manufactured in Example 1, the MZM type light intensity modulator 206 according to the sixth embodiment was manufactured. In the fabricated MZM type optical intensity modulator, it was confirmed that optical intensity modulation at 40 Gbps or higher and transmission of the modulated optical signal were possible, which was the same as that of a practical optical communication system.
  • Silicon-based electro-optics that realize an optical modulator structure based on the carrier plasma effect that can achieve low cost, low current density, low power consumption, high modulation depth, low voltage drive, and high-speed modulation in the submicron region An apparatus can be provided.

Abstract

This silicon-based electro-optical device is characterized in that, in a region where silicon semiconductor layers of a first and second conductor type are laminated, an uneven portion comprising a Si1-xGex layer (x=0.01-0.9) is provided on the surface of a first silicon semiconductor layer, a comparatively thin inductive body is formed thereon, and further laminated is a silicon semiconductor layer of the second conductor type.

Description

シリコンベース電気光学装置Silicon-based electro-optic device
　本発明は、情報処理および通信分野において必要となる、高速電気信号を光信号に高速に変換するシリコンベース電気光学装置に関するものであり、より詳細には、充分な高速動作を行うように、シリコン－オン－インシュレータ（ＳＯＩ：ｓｉｌｉｃｏｎ　ｏｎ　ｉｎｓｕｌａｔｏｒ）基板上に形成された、シリコン－絶縁体－シリコンからなるキャパシタ構造を利用したシリコンベース電気光学装置に関する。 The present invention relates to a silicon-based electro-optical device that converts a high-speed electrical signal into an optical signal at high speed, which is necessary in the information processing and communication fields. The present invention relates to a silicon-based electro-optical device using a silicon-insulator-silicon capacitor structure formed on an on-insulator (SOI) substrate.
　家庭用光ファイバおよびローカルエリアネットワーク（ＬＡＮ：ｌｏｃａｌ　ａｒｅａ　ｎｅｔｗｏｒｋ）などの様々なシステムにおいて、１３３０ｎｍあるいは１５００ｎｍの光ファイバ通信波長で機能するシリコンベース光通信デバイスは、ＣＭＯＳ（ｃｏｍｐｌｅｍｅｎｔａｒｙ　ｍｅｔａｌ　ｏｘｉｄｅ　ｓｅｍｉｃｏｎｄｕｃｔｏｒ）技術を利用して、光機能素子および電子回路をシリコンプラットフォーム上に集積化可能とする非常に有望な技術である。 In various systems such as home optical fiber and local area network (LAN), silicon-based optical communication devices that function at 1330 nm or 1500 nm optical fiber communication wavelengths use CMOS (complementary metal oxide semiconductor) technology. Thus, this is a very promising technology that enables an optical functional element and an electronic circuit to be integrated on a silicon platform.
　近年、シリコンベースの導波路、光結合器、および波長フィルタなどの受動デバイスが、広く研究されている。また、通信システム用の光信号を操作可能とする重要な技術として、シリコンベースの光変調器や光スイッチなどの能動デバイスが挙げられ、非常に注目されている。しかしながら、シリコンの熱光学効果を利用して屈折率を変化させる光変調器や光スイッチは、低速であり、１Ｍｂｐｓの変調周波数までの装置速度においてしか使用出来ない。従って、より多くの光通信システムに要求される高い変調周波数を実現するためには、高速動作を可能とする電気光学効果を利用した光変調器や光スイッチが求められる。 In recent years, passive devices such as silicon-based waveguides, optical couplers, and wavelength filters have been widely studied. In addition, active devices such as silicon-based optical modulators and optical switches are attracting much attention as important techniques for enabling the manipulation of optical signals for communication systems. However, optical modulators and optical switches that change the refractive index using the thermo-optic effect of silicon are slow and can only be used at device speeds up to a modulation frequency of 1 Mbps. Therefore, in order to realize a high modulation frequency required for more optical communication systems, an optical modulator or an optical switch using an electro-optical effect that enables high-speed operation is required.
　純シリコンは、線形電気光学効果（Ｐｏｃｋｅｌｓ効果）を示さず、Ｆｒａｎｚ－Ｋｅｌｄｙｓｈ効果やＫｅｒｒ効果による純シリコンの屈折率の変化は非常に小さい。そのため、現在提案されている電気光学変調器の多くは、キャリアプラズマ効果を利用して、シリコン層中の自由キャリア密度を変化させることにより、屈折率の実数部と虚数部を変化させ、シリコン層を伝播する光の位相や強度を変化させる。このような自由キャリア吸収を利用した変調器では、シリコン層内を伝播する光の吸収の変化により、出力光の強度が直接変調される。また、屈折率変化を利用した構造としては、マッハ－ツェンダー干渉計を利用したものが一般的である。導波路型のマッハ－ツェンダー干渉計では、前記屈折率変化によって２本のアームを伝播する一方または両方の光に位相差を与え、これらの光を干渉させることにより、光の強度変調信号が得られる。 Pure silicon does not exhibit a linear electro-optic effect (Pockels effect), and the change in refractive index of pure silicon due to the Franz-Keldysh effect or the Kerr effect is very small. For this reason, many of the electro-optic modulators currently proposed change the real part and the imaginary part of the refractive index by changing the free carrier density in the silicon layer by utilizing the carrier plasma effect. The phase and intensity of light propagating through the light is changed. In such a modulator using free carrier absorption, the intensity of output light is directly modulated by a change in absorption of light propagating in the silicon layer. In general, a structure using a Mach-Zehnder interferometer is used as a structure using the refractive index change. In the waveguide type Mach-Zehnder interferometer, a phase difference is given to one or both of the lights propagating through the two arms due to the refractive index change, and these lights are made to interfere with each other, thereby obtaining an intensity modulation signal of the light. It is done.
　電気光学変調器における自由キャリア密度は、自由キャリアの注入、蓄積、除去、または反転によって変えることが出来る。しかしながら、既に検討されている電気光学変調器の多くは、光変調効率が悪く、光位相変調に必要な長さ（以降、単に「光位相変調長」と称する）がｍｍオーダーであり、１ｋＡ／ｃｍ３より高い注入電流密度を必要とする。電気光学変調器の光位相変調長が長く、素子サイズが大きくなると、シリコンプラットフォーム上での温度分布の影響を受け易くなり、熱光学効果に起因するシリコン層の屈折率変化により、本来の電気光学効果が打ち消されるおそれがある。従って、電気光学変調器の小型・高集積化、及び低消費電力化を実現するためには、高い光変調効率が得られる素子構造が求められる。 The free carrier density in the electro-optic modulator can be changed by free carrier injection, accumulation, removal, or inversion. However, many of the electro-optic modulators that have already been studied have poor optical modulation efficiency, and the length necessary for optical phase modulation (hereinafter simply referred to as “optical phase modulation length”) is on the order of 1 mm, An injection current density higher than cm 3 is required. If the optical phase modulation length of the electro-optic modulator is long and the element size is large, it becomes more susceptible to the temperature distribution on the silicon platform, and the original electro-optic due to the refractive index change of the silicon layer due to the thermo-optic effect. The effect may be countered. Therefore, in order to realize a small size, high integration, and low power consumption of the electro-optic modulator, an element structure capable of obtaining high light modulation efficiency is required.
　上記要求を満たす電気光学変調器として、例えば非特許文献１には、ＳＯＩ基板上にリブ導波路構造を備えたシリコンベース電気光学装置が開示されている。非特許文献１に記載のシリコンベース電気光学装置では、真性半導体領域からなるリブ導波路構造の両側横方向に延びるスラブ領域がｐタイプ、ｎタイプにそれぞれドープされている。 As an electro-optic modulator that satisfies the above requirements, for example, Non-Patent Document 1 discloses a silicon-based electro-optic device having a rib waveguide structure on an SOI substrate. In the silicon-based electro-optical device described in Non-Patent Document 1, slab regions extending laterally on both sides of a rib waveguide structure made of an intrinsic semiconductor region are doped in p-type and n-type, respectively.
　上記リブ導波路構造は、図１４に示すように、シリコンからなる支持基板３、埋め込み酸化層２を含むＳＯＩ基板上のシリコン層１Ｓを利用して形成される。リブ導波路構造は、ＰＩＮダイオード型変調器であり、順方向および逆方向バイアスを印加することにより、真性半導体領域内の自由キャリア密度を変化させ、キャリアプラズマ効果を利用することにより、屈折率を変化させる構造となっている。図１４のＰＩＮダイオード型変調器では、真性半導体シリコン１が、第１の電極コンタクト層６Ａと接触するシリコン層１Ｓに高濃度にドープ処理されてなるｐ＋ドープ半導体シリコン４を含むように形成されている。また、真性半導体シリコン１は、シリコン層１Ｓに対して高濃度にドープ処理されたｎ＋ドープ半導体シリコン５および、これに接続する第２の電極コンタクト層６Ｂを含む。
ｐ＋およびｎ＋ドープ半導体シリコン４，５は、１ｃｍ３毎に約１０２０のキャリア密度を呈するようにドープ処理される。 As shown in FIG. 14, the rib waveguide structure is formed using a silicon layer 1S on an SOI substrate including a support substrate 3 made of silicon and a buried oxide layer 2. The rib waveguide structure is a PIN diode type modulator that changes the free carrier density in the intrinsic semiconductor region by applying forward and reverse biases, and uses the carrier plasma effect to change the refractive index. It has a changing structure. In the PIN diode type modulator of FIG. 14, intrinsic semiconductor silicon 1 is formed so as to include p + doped semiconductor silicon 4 formed by highly doping silicon layer 1S in contact with first electrode contact layer 6A. Yes. In addition, intrinsic semiconductor silicon 1 includes n + doped semiconductor silicon 5 that is highly doped with respect to silicon layer 1S, and second electrode contact layer 6B connected thereto.
The p + and n + doped semiconductor silicon 4, 5 is doped to exhibit a carrier density of about 10 20 per cm 3 .
　図１４に示すリブ導波路構造では、第１および第２の電極コンタクト層６Ａ，６Ｂが電極配線７を介して電源（図示略）に接続されている。第１および第２の電極コンタクト層６Ａ，６Ｂを用いて、ＰＩＮダイオードに対して順方向バイアスを印加することにより、導波路内に自由キャリアが注入される。そして、自由キャリアの増加により、真性半導体シリコン１の屈折率が変化し、それによって導波路内を伝播する光の位相変調が行われる。 In the rib waveguide structure shown in FIG. 14, the first and second electrode contact layers 6 </ b> A and 6 </ b> B are connected to a power source (not shown) through the electrode wiring 7. By applying a forward bias to the PIN diode using the first and second electrode contact layers 6A and 6B, free carriers are injected into the waveguide. Then, due to the increase in free carriers, the refractive index of the intrinsic semiconductor silicon 1 changes, whereby phase modulation of light propagating in the waveguide is performed.
　また、別の電気光学変調器として、例えば特許文献１には、ＳＯＩプラットフォーム上に形成されたＳＩＳ（ｓｉｌｉｃｏｎ－ｉｎｓｌａｔｏｒ－ｓｉｌｉｃｏｎ）型構造を備えたシリコンベース電気光学装置が開示されている。特許文献１に記載のシリコンベース電気光学装置は、図１５に示すように、ＳＯＩ基板の比較的薄いシリコン表面層に形成された本体領域であるｎドープ多結晶シリコン１０と、ｎドープ多結晶シリコン１０と部分的に重なるように積層されたゲート領域であるｐドープ半導体シリコン９からなる。また、ｐドープ半導体シリコン９とｎドープ多結晶シリコン１０との積層界面には、比較的薄い誘電体層１２が形成されている。ゲート領域及び本体領域内にドープ処理されてなるｐ，ｎドープ多結晶シリコン９，１０は、キャリア密度変化が外部信号電圧により電極配線７及びｐ＋，ｎ＋ドープ半導体シリコン４，１１を介して制御されるように規定されている。 As another electro-optic modulator, for example, Patent Document 1 discloses a silicon-based electro-optic device having a SIS (silicon-insulator-silicon) type structure formed on an SOI platform. As shown in FIG. 15, a silicon-based electro-optical device described in Patent Document 1 includes an n-doped polycrystalline silicon 10 that is a main body region formed on a relatively thin silicon surface layer of an SOI substrate, and an n-doped polycrystalline silicon. 10 is made of p-doped semiconductor silicon 9 which is a gate region laminated so as to partially overlap with 10. A relatively thin dielectric layer 12 is formed at the laminated interface between the p-doped semiconductor silicon 9 and the n-doped polycrystalline silicon 10. In the p and n doped polycrystalline silicon 9 and 10 doped in the gate region and the main body region, the carrier density change is controlled by the external signal voltage via the electrode wiring 7 and the p + and n + doped semiconductor silicon 4 and 11. It is stipulated that
特表２００６－５１５０８２号公報Special table 2006-515082 gazette
　非特許文献１に記載のシリコンベース電気光学装置の動作速度は、真性半導体シリコン１内の自由キャリア寿命と、順方向バイアスが取り除かれた場合のキャリア拡散によって制限される。このように、関連技術のＰＩＮダイオード型変調器は、通常、順方向バイアス動作時に１０～５０Ｍｂｐｓの範囲内の動作速度を有する。これに対し、キャリア寿命を短くするために、真性半導体シリコン１内に不純物を導入することによって、切り換え速度を増加させることは可能であるが、導入された不純物は光変調効率を低下させてしまう。また、ＰＩＮダイオード型変調器の動作速度に影響する最も大きな因子は、ＲＣ時定数であり、上記リブ導波路構造の場合、順方向バイアス印加時の静電容量（Ｃ）が、ＰＮ接合部のキャリア空乏層の減少により非常に大きくなる。ＰＮ接合部の高速動作は、理論的には、逆バイアスを印加することにより達成できるが、駆動電圧が比較的大きくなってしまう、あるいはシリコンベース電気光学装置のサイズが大きくなってしまう問題があった。 The operating speed of the silicon-based electro-optical device described in Non-Patent Document 1 is limited by the free carrier lifetime in intrinsic semiconductor silicon 1 and carrier diffusion when the forward bias is removed. Thus, related art PIN diode modulators typically have operating speeds in the range of 10-50 Mbps during forward bias operation. On the other hand, in order to shorten the carrier life, it is possible to increase the switching speed by introducing impurities into the intrinsic semiconductor silicon 1, but the introduced impurities reduce the light modulation efficiency. . The largest factor that affects the operating speed of the PIN diode type modulator is the RC time constant. In the case of the rib waveguide structure, the electrostatic capacity (C) when a forward bias is applied is equal to that of the PN junction. It becomes very large due to the reduction of the carrier depletion layer. High speed operation of the PN junction can theoretically be achieved by applying a reverse bias, but there is a problem that the drive voltage becomes relatively large or the size of the silicon-based electro-optical device becomes large. It was.
　また、特許文献１に記載のシリコンベース電気光学装置においては、光信号電界とキャリア密度が動的に外部制御される領域は一致することが望ましい。光信号電界とキャリア密度の外部制御領域が一致した場合、誘電体層１２の両側で、自由キャリアが蓄積、除去、または反転することにより、光位相変調がなされる。しかしながら、実際には、キャリア密度が動的に変化する領域は数十ｎｍ程度と非常に薄くなってしまう。このため、ｍｍオーダーの光位相変調長が必要となり、結果として、シリコンベース電気光学装置が大型化するとともに、高速動作が難くなってしまう問題があった。 Also, in the silicon-based electro-optical device described in Patent Document 1, it is desirable that the optical signal electric field and the region where the carrier density is dynamically controlled externally match. When the optical signal electric field and the external control region of the carrier density coincide with each other, optical phase modulation is performed by accumulating, removing, or inverting free carriers on both sides of the dielectric layer 12. However, in practice, the region where the carrier density changes dynamically becomes as thin as about several tens of nanometers. For this reason, an optical phase modulation length on the order of mm is required. As a result, there is a problem that the silicon-based electro-optical device becomes large and high-speed operation becomes difficult.
　本発明は、上述の問題を解決し、シリコン基板上に集積化可能なシリコンベース電気光学装置において、低電流密度、低消費電力、高い変調度、低電圧駆動、および高速変調を、サブミクロンの領域内で実現可能な、キャリアプラズマ効果に基づく光変調器構造を低コストで実現することのできるシリコンベース電気光学装置を提供することにある。 The present invention solves the above-described problems, and achieves low current density, low power consumption, high modulation degree, low voltage drive, and high-speed modulation in a submicron in a silicon-based electro-optical device that can be integrated on a silicon substrate. An object of the present invention is to provide a silicon-based electro-optical device capable of realizing an optical modulator structure based on the carrier plasma effect, which can be realized in a region, at a low cost.
　本発明のシリコンベース電気光学装置は、第１の導電タイプを呈するようにドープ処理されたシリコン半導体層と第２の導電タイプを呈するようにドープ処理されたシリコン半導体層の少なくとも一部が積層された構造からなり、前記積層された半導体層の界面に、比較的薄い誘電体が形成されたＳＩＳ型接合において、前記第１および第２のドープ領域に結合された電気端子からの電気信号により、自由キャリアが、前記比較的薄い誘導体の両側で蓄積、除去、または反転することにより、光信号電界に作用する自由キャリア濃度が変調されることを利用した電気光学装置であって、前記第１および第２の導電タイプを呈するシリコン半導体層が積層された領域において、前記第１のシリコン半導体層表面にＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が設けられており、この上に比較的薄い誘電体が形成され、さらに前記第２の導電タイプを呈するシリコン半導体層が積層されていることを特徴とする。 The silicon-based electro-optical device according to the present invention is formed by laminating at least a part of a silicon semiconductor layer doped to exhibit the first conductivity type and a silicon semiconductor layer doped to exhibit the second conductivity type. In an SIS type junction in which a relatively thin dielectric is formed at the interface of the stacked semiconductor layers, by an electrical signal from an electrical terminal coupled to the first and second doped regions, An electro-optical device utilizing the fact that free carrier concentration is modulated on free signal concentration acting on an optical signal electric field by accumulation, removal, or inversion on both sides of the relatively thin derivative, In the region where the silicon semiconductor layer exhibiting the second conductivity type is stacked, Si 1-x Ge x (x = 0. (01-0.9) is provided with unevenness, a relatively thin dielectric is formed thereon, and a silicon semiconductor layer exhibiting the second conductivity type is further laminated. .
　本発明のシリコンベース電気光学装置によれば、低電流密度、低消費電力、高い変調度、低電圧駆動、および高速変調を、サブミクロンの領域内で実現可能な、キャリアプラズマ効果に基づく光変調器構造を低コストで実現することができる。 According to the silicon-based electro-optical device of the present invention, light modulation based on the carrier plasma effect that can realize low current density, low power consumption, high modulation degree, low voltage drive, and high-speed modulation in the submicron region. The vessel structure can be realized at low cost.
本発明の第１実施形態に係るシリコンベース電気光学装置の断面図である。1 is a cross-sectional view of a silicon-based electro-optical device according to a first embodiment of the invention. 本発明の第１実施形態に係るシリコンベース電気光学装置の平面図であり、光伝播方向における平面図である。1 is a plan view of a silicon-based electro-optical device according to a first embodiment of the present invention, and is a plan view in a light propagation direction. FIG. 本発明の第２実施形態に係るシリコンベース電気光学装置の断面図である。FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a second embodiment of the invention. 本発明の第３実施形態に係るシリコンベース電気光学装置の断面図である。FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a third embodiment of the invention. 本発明の第４実施形態に係るシリコンベース電気光学装置の断面図である。FIG. 6 is a cross-sectional view of a silicon-based electro-optical device according to a fourth embodiment of the invention. 本発明の第５実施形態に係るシリコンベース電気光学装置の断面図である。FIG. 10 is a cross-sectional view of a silicon-based electro-optical device according to a fifth embodiment of the invention. 本発明の第５実施形態に係るシリコンベース電気光学装置の平面図であり、光伝播方向における平面図である。FIG. 10 is a plan view of a silicon-based electro-optical device according to a fifth embodiment of the invention, and is a plan view in the light propagation direction. 本発明の第１実施形態に係るシリコンベース電気光学装置の製造工程を示す断面図である。It is sectional drawing which shows the manufacturing process of the silicon base electro-optical apparatus which concerns on 1st Embodiment of this invention. 本発明の第６実施形態に係るマッハ－ツェンダー干渉計型の構造を説明するための平面図である。It is a top view for demonstrating the structure of the Mach-Zehnder interferometer type | mold which concerns on 6th Embodiment of this invention. 本発明の第７実施形態に係るマッハ－ツェンダー干渉計型の構造を説明するための平面図である。It is a top view for demonstrating the structure of the Mach-Zehnder interferometer type | mold which concerns on 7th Embodiment of this invention. 本発明の第８実施形態に係るマッハ－ツェンダー干渉計型の構造を説明するための平面図である。It is a top view for demonstrating the structure of the Mach-Zehnder interferometer type | mold which concerns on 8th Embodiment of this invention. 実施例１におけるシリコンベース電気光学装置の光位相シフト量の光位相変調長依存性を示すグラフである。6 is a graph showing the optical phase modulation length dependence of the optical phase shift amount of the silicon-based electro-optical device in Example 1. 実施例１におけるシリコンベース電気光学装置の光位相シフト量の動作周波数帯域依存性を示すグラフである。6 is a graph showing the operating frequency band dependency of the optical phase shift amount of the silicon-based electro-optical device in Example 1. 非特許文献１に開示されているシリコンベース電気光学装置の断面図である。1 is a cross-sectional view of a silicon-based electro-optical device disclosed in Non-Patent Document 1. FIG. 特許文献１に開示されているシリコンベース電気光学装置の断面図である。1 is a cross-sectional view of a silicon-based electro-optical device disclosed in Patent Document 1. FIG.
　以下、本発明の実施形態であるシリコンベース電気光学装置およびマッハ－ツェンダー干渉計型の構造について、図面を参照して詳細に説明する。
　なお、以下の説明で用いる図面は、特徴をわかりやすくするために、便宜上特徴となる部分を拡大して示している場合があり、各構成要素の寸法比率などが実際と同じであるとは限らない。 Hereinafter, a silicon-based electro-optical device and a Mach-Zehnder interferometer type structure according to an embodiment of the present invention will be described in detail with reference to the drawings.
In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.
　図１～図１３に示す本発明の実施形態のシリコンベース電気光学装置は、電気光学効果（自由キャリアプラズマ効果）を利用するものである。以下に、本発明のシリコンベース電気光学装置における動作原理である、シリコン内の光位相変調メカニズムの概要を説明する。 The silicon-based electro-optical device according to the embodiment of the present invention shown in FIGS. 1 to 13 utilizes an electro-optical effect (free carrier plasma effect). The outline of the optical phase modulation mechanism in silicon, which is the principle of operation in the silicon-based electro-optical device of the present invention, will be described below.
（自由キャリアプラズマ効果の概要）
　前述したように、純粋な電気光学効果はシリコン内には存在しない、または非常に弱いため、自由キャリアプラズマ効果と熱光学効果のみがシリコンベース電気光学装置の光変調動作に用いられる。すなわち、シリコンベース電気光学装置において、本発明が目的とするＧｂｐｓ以上の高速動作を実現するためには、自由キャリアプラズマ効果のみが効果的である。自由キャリアプラズマ効果は、下記の式（１），（２）の１次近似値で説明される。 (Outline of free carrier plasma effect)
As described above, since the pure electro-optic effect does not exist in silicon or is very weak, only the free carrier plasma effect and the thermo-optic effect are used for the light modulation operation of the silicon-based electro-optic device. That is, in the silicon-based electro-optical device, only the free carrier plasma effect is effective in order to realize a high-speed operation of Gbps or more which is the object of the present invention. The free carrier plasma effect is explained by a first order approximation of the following formulas (1) and (2).
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　式（１），（２）において、ΔｎおよびΔｋは、シリコン半導体層の屈折率変化の実部および虚部を表わしており、ｅは電荷、λは光の波長、ε０は真空中の誘電率、ｎは真性半導体シリコンの屈折率、ｍeは電子キャリアの有効質量、ｍhはホールキャリアの有効質量、μeは電子キャリアの移動度、μhはホールキャリアの移動度、ΔＮeは電子キャリアの濃度変化、ΔＮhはホールキャリアの濃度変化である。 In equations (1) and (2), Δn and Δk represent the real part and the imaginary part of the refractive index change of the silicon semiconductor layer, e is the charge, λ is the wavelength of light, and ε 0 is the dielectric in vacuum. , N is the refractive index of intrinsic semiconductor silicon, m e is the effective mass of the electron carrier, m h is the effective mass of the hole carrier, μ e is the mobility of the electron carrier, μ h is the mobility of the hole carrier, and ΔN e is The electron carrier concentration change, ΔN h is the hole carrier concentration change.
　Ｓｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層（以降、単にＳｉ１－ｘＧｅｘ層と記載する）においては、Ｇｅの組成ｘを増加させることにより、電子およびホールキャリアの有効質量が小さくなり、より大きな屈折率変化量を得ることが可能である。また、屈折率の虚部、すなわち光吸収係数も大きくなる。従って、電気光学変調器においては、Ｓｉ１－ｘＧｅｘ層を凹凸状に形成し、自由キャリア密度が変化する領域と光フィールドとのオーバーラップを改善し、アクティブ層の長さを小さくすることが重要である。 In a Si 1-x Ge x (x = 0.01 to 0.9) layer (hereinafter simply referred to as a Si 1-x Ge x layer), an electron and hole carrier can be obtained by increasing the Ge composition x. It is possible to obtain a larger amount of change in the refractive index. In addition, the imaginary part of the refractive index, that is, the light absorption coefficient also increases. Therefore, in the electro-optic modulator, the Si 1-x Ge x layer is formed in a concavo-convex shape, the overlap between the region where the free carrier density changes and the optical field is improved, and the length of the active layer is reduced. is important.
　Ｓｉ１－ｘＧｅｘ層は、シリコン半導体層に比べて屈折率が大きいため、自由キャリア密度が変化する領域と光フィールドとのオーバーラップを改善する効果がある。さらに、上記のようにＳｉ１－ｘＧｅｘ層を凹凸形状とすることにより、アクティブ層の長さを顕著に小さくすることが可能である。 Since the Si 1-x Ge x layer has a higher refractive index than the silicon semiconductor layer, there is an effect of improving the overlap between the region where the free carrier density changes and the optical field. Furthermore, the length of the active layer can be remarkably reduced by making the Si 1-x Ge x layer uneven as described above.
　また、Ｓｉ１－ｘＧｅｘ層におけるＧｅの組成を高めることにより、自由キャリアプラズマ効果が、よりエンハンスされる。光通信システムで使用する波長１３１０ｎｍおよび１５５０ｎｍにおいては、Ｓｉ１－ｘＧｅｘ層中の電子エネルギー遷移に起因する光吸収を避けるために、Ｇｅの組成はｘ＝０．０１～０．９であることが好ましい。また、Ｓｉ１－ｘＧｅｘ層に歪を印加することにより、電子およびホールキャリアの有効質量がより小さくなり、より大きな自由キャリアプラズマ効果を得ることができる。 Further, the free carrier plasma effect is further enhanced by increasing the Ge composition in the Si 1-x Ge x layer. At wavelengths of 1310 nm and 1550 nm used in the optical communication system, the composition of Ge is x = 0.01 to 0.9 in order to avoid light absorption due to electronic energy transition in the Si 1-x Ge x layer. It is preferable. Further, by applying strain to the Si 1-x Ge x layer, the effective masses of electrons and hole carriers are reduced, and a larger free carrier plasma effect can be obtained.
　シリコン中の電気光学効果の実験的な評価が行われており、光通信システムで使用する波長１３１０ｎｍおよび１５５０ｎｍでのキャリア密度に対する屈折率変化は、Ｄｒｕｄｅの式と良く一致することが知られている。また、Ｄｒｕｄｅの式に基づく光学的動作を利用した電気光学変調器においては、位相変化量は次式（３）で定義される。 Experimental evaluation of the electro-optic effect in silicon has been performed, and it is known that the refractive index change with respect to the carrier density at wavelengths of 1310 nm and 1550 nm used in the optical communication system agrees well with the Drude equation. . In an electro-optic modulator that uses an optical operation based on the Drude equation, the phase change amount is defined by the following equation (3).
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　式（３）におけるＬは、シリコンベース電気光学装置の光伝播方向に沿ったアクティブ層の長さである。 L in Equation (3) is the length of the active layer along the light propagation direction of the silicon-based electro-optical device.
　本発明では、上記位相変化量は光吸収と比較して大きな効果として発揮される。以下で説明するシリコンベース電気光学装置は、基本的に位相変調器としての特徴を示すことが出来る。 In the present invention, the amount of phase change is exerted as a great effect as compared with light absorption. The silicon-based electro-optical device described below can basically exhibit characteristics as a phase modulator.
　次に、図１～図１１を参照しながら、上述の自由キャリアプラズマ効果を用いた、ＳＩＳ接合からなる本発明のシリコンベース電気光学装置について説明する。 Next, a silicon-based electro-optical device according to the present invention that is formed of a SIS junction using the above-described free carrier plasma effect will be described with reference to FIGS.
（第１実施形態）
　本発明を適用した第１実施形態に係る電気光学位相変調器（シリコンベース電気光学装置）１０１の断面図を図１に示す。
　電気光学位相変調器１０１は、Ｓｉ１－ｘＧｅｘ層からなる凹凸（以降、単に「Ｓｉ１－ｘＧｅｘ凹凸層」と称する）１３と、比較的薄い誘電体層（誘電体）１２と、ｎドープ多結晶シリコン（第２の導電タイプを呈するシリコン半導体層）１０と、を有する。また、電気光学位相変調器１０１は、支持基板３、埋め込み酸化層２、ｐドープ多結晶シリコン（第１の導電タイプを呈するシリコン半導体層）９が順次積層されてなるＳＯＩ基板上に形成されている。なお、図１では、ｎドープ多結晶シリコン１０のうち、誘電体層１２に接する部分をｎドープ多結晶シリコン１９として図示している。 (First embodiment)
FIG. 1 shows a cross-sectional view of an electro-optic phase modulator (silicon-based electro-optic device) 101 according to the first embodiment to which the present invention is applied.
Electro-optic phase modulator 101, Si 1-x Ge x consisting layer irregularities (hereinafter, simply referred to as "Si 1-x Ge x uneven layer") 13, a relatively thin dielectric layer (dielectric) 12 and N-doped polycrystalline silicon (silicon semiconductor layer exhibiting the second conductivity type) 10. The electro-optic phase modulator 101 is formed on an SOI substrate in which a support substrate 3, a buried oxide layer 2, and p-doped polycrystalline silicon (a silicon semiconductor layer exhibiting the first conductivity type) 9 are sequentially stacked. Yes. In FIG. 1, a portion of the n-doped polycrystalline silicon 10 that is in contact with the dielectric layer 12 is illustrated as an n-doped polycrystalline silicon 19.
　ここで、本発明においては、前記比較的薄い誘電体層１２が、酸化シリコン、窒化シリコン、酸化ハフニウム、酸化ジルコニウム、酸化アルミニウムの少なくとも一層からなることを特徴とする。また、前記比較的薄い誘電体層１２の層厚が、０．１ｎｍから５０ｎｍであることを特徴とする。前記比較的薄い誘電体は、電気光学位相変調器１０１においては、誘電体層１２の両側で自由キャリアを蓄積させる際において、誘電率を大きくすると共に、膜厚を薄くすることにより、変調効率が改善されることになる。一方、電気容量の増加は、高速動作する際に周波数帯域を減少させることになるため、目的とする変調効率と高速性を実現するために最適な膜厚および材料が適用される。膜厚に関しては、０．１ｎｍより薄くなると実用上リーク電流の問題があり、また５０ｎｍより厚くなると変調効率が大幅に低下するため、０．１ｎｍ以上５０ｎｍ以下の範囲で設計することが好ましい。 Here, the present invention is characterized in that the relatively thin dielectric layer 12 is composed of at least one layer of silicon oxide, silicon nitride, hafnium oxide, zirconium oxide, and aluminum oxide. Further, the relatively thin dielectric layer 12 has a thickness of 0.1 nm to 50 nm. In the electro-optic phase modulator 101, the relatively thin dielectric increases the dielectric constant and reduces the film thickness when free carriers are accumulated on both sides of the dielectric layer 12, thereby improving the modulation efficiency. It will be improved. On the other hand, an increase in electric capacity decreases the frequency band during high-speed operation, and therefore an optimum film thickness and material are applied to achieve the target modulation efficiency and high speed. Regarding the film thickness, if it is thinner than 0.1 nm, there is a practical problem of leakage current, and if it is thicker than 50 nm, the modulation efficiency is greatly reduced. Therefore, it is preferable to design in the range of 0.1 nm to 50 nm.
　Ｓｉ１－ｘＧｅｘ凹凸層１３は、ＳＯＩ基板のｐドープ半導体シリコン９の表面に設けられている。Ｇｅの組成は、自由キャリアプラズマ効果を高めるために、ｘ＝０．０１～０．９とすることが好ましい。 The Si 1-x Ge x concavo-convex layer 13 is provided on the surface of the p-doped semiconductor silicon 9 of the SOI substrate. The composition of Ge is preferably x = 0.01 to 0.9 in order to enhance the free carrier plasma effect.
　比較的薄い誘電体層１２は、Ｓｉ１－ｘＧｅｘ凹凸層１３及びＳＯＩ層の表面上の一部に形成されている。従って、Ｓｉ１－ｘＧｅｘ凹凸層１３の最上面だけではなく側面、くぼみのあらゆる露出面が誘電体層１２で覆われている。 The relatively thin dielectric layer 12 is formed on a part of the surface of the Si 1-x Ge x uneven layer 13 and the SOI layer. Therefore, not only the uppermost surface of the Si 1-x Ge x concavo-convex layer 13 but all exposed surfaces of the side surfaces and the depressions are covered with the dielectric layer 12.
　ｎドープ多結晶シリコン１０は、誘電体層１２上の表面凹凸を被覆するように積層されている。また、光学的損失を低減するために、ｎドープ多結晶シリコン１０の表面はポリッシングにより平滑化されても良い。
　ｐ及びｎドープ多結晶シリコン９，１０には、それぞれに外部から駆動電圧を印加するための電極配線７が接続されている。また、ｐ及びｎドープ多結晶シリコン９，１０と電極配線７のそれぞれの接続部分には、高濃度ドープ処理されたｐ＋及びｎ＋ドープ半導体シリコン４，１１が形成されている。なお、ｐ＋及びｎ＋ドープ半導体シリコン４，１１は、電極配線７のコンタクトとして機能するが、必要に応じてｐ＋及びｎ＋ドープ半導体シリコン４，１１と電極配線７との界面に、各々コンタクト層６を設けてもよい。
　ｐ及びｎドープ多結晶シリコン９，１０は、多結晶シリコン、アモルファスシリコン、歪シリコン、単結晶シリコン、Ｓｉ１－ｘＧｅｘからなる群から選択される少なくとも一層からなる。 The n-doped polycrystalline silicon 10 is laminated so as to cover the surface irregularities on the dielectric layer 12. In order to reduce optical loss, the surface of the n-doped polycrystalline silicon 10 may be smoothed by polishing.
An electrode wiring 7 for applying a driving voltage from the outside is connected to each of the p and n doped polycrystalline silicons 9 and 10. Further, p + and n + doped semiconductor silicons 4 and 11 subjected to high concentration doping are formed at connection portions between the p and n doped polycrystalline silicons 9 and 10 and the electrode wiring 7. The p + and n + doped semiconductor silicons 4 and 11 function as contacts of the electrode wiring 7, but the contact layers 6 are respectively provided at the interfaces between the p + and n + doped semiconductor silicon 4 and 11 and the electrode wiring 7 as necessary. It may be provided.
The p- and n-doped polycrystalline silicons 9 and 10 are composed of at least one layer selected from the group consisting of polycrystalline silicon, amorphous silicon, strained silicon, single crystal silicon, and Si 1-x Ge x .
　電気光学位相変調器１０１では、ＳＩＳ接合界面にＳｉ１－ｘＧｅｘ凹凸層１３を設けることにより、光フィールドとキャリア密度変調領域のオーバーラップが大きくなる。また、Ｓｉ１－ｘＧｅｘ層１３を採用することにより、シリコン半導体層よりも大きなキャリアプラズマ効果が得られるため、電気光学位相変調器１０１のサイズを小さくすることができる。また、ＳＩＳ接合界面に隣接するｐ，ｎドープ多結晶シリコン９，１０のドーピング密度をさらに上昇させることにより、直列抵抗成分を小さくし、ＲＣ時定数を小さくすることができる。 In the electro-optic phase modulator 101, by providing the Si 1-x Ge x uneven layer 13 at the SIS junction interface, the overlap between the optical field and the carrier density modulation region is increased. Further, by adopting the Si 1-x Ge x layer 13, a larger carrier plasma effect than that of the silicon semiconductor layer can be obtained, so that the size of the electro-optic phase modulator 101 can be reduced. Further, by further increasing the doping density of the p and n doped polycrystalline silicon 9 and 10 adjacent to the SIS junction interface, the series resistance component can be reduced and the RC time constant can be reduced.
　また、電気光学位相変調器１０１においては、ｐ，ｎドープ多結晶シリコン９，１０のドーピング密度を上昇させた領域と光フィールドとのオーバーラップによる光吸収損失を低減するために、ＳＩＳ接合の部分を図１に示すようなリブ／リッジ形状からなる導波路形状とする。そして、スラブ領域のドーピング密度を上昇させた構造とすることにより、光損失およびＲＣ時定数が小さく、高速動作可能な電気光学位相変調器を実現することができる。 Further, in the electro-optic phase modulator 101, in order to reduce the light absorption loss due to the overlap between the region where the doping density of the p and n doped polycrystalline silicon 9 and 10 is increased and the optical field, Is a waveguide having a rib / ridge shape as shown in FIG. In addition, by adopting a structure in which the doping density of the slab region is increased, an electro-optic phase modulator capable of operating at high speed with small optical loss and RC time constant can be realized.
　上記のように、ＳＩＳ接合界面に設けられた凹凸は、ｐドープ半導体シリコン９表面にＳｉ１－ｘＧｅｘ凹凸層１３を形成し、さらに誘電体層１２、その上にｎドープ多結晶シリコン１０を積層して形成することにより実現される。Ｓｉ１－ｘＧｅｘ凹凸層１３における凹凸の間隔（周期）は、自由キャリアが誘電体層１２の両側で蓄積、除去、または反転する半導体層の厚さ（以下、最大空乏層厚）Ｗに対して、２Ｗ以下であることが好ましい。２Ｗ以上であっても変調効率を改善する効果は得られるが、変調効率を改善する効果をより高めるためには２Ｗ以下であることが好ましい。 As described above, the unevenness provided at the SIS junction interface is formed by forming the Si 1-x Ge x uneven layer 13 on the surface of the p-doped semiconductor silicon 9, the dielectric layer 12, and the n-doped polycrystalline silicon 10 on the dielectric layer 12. This is realized by stacking the layers. The unevenness interval (period) in the Si 1-x Ge x uneven layer 13 is equal to the thickness (hereinafter referred to as the maximum depletion layer thickness) W of the semiconductor layer in which free carriers are accumulated, removed, or inverted on both sides of the dielectric layer 12. On the other hand, it is preferably 2 W or less. Although the effect of improving the modulation efficiency can be obtained even if it is 2 W or more, it is preferably 2 W or less in order to further enhance the effect of improving the modulation efficiency.
　熱平衡状態における最大空乏層厚Ｗは、次式（４）で与えられる。 The maximum depletion layer thickness W in the thermal equilibrium state is given by the following equation (4).
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　式（４）において、εｓは半導体層の誘電率、ｋはボルツマン定数、Ｎｃはキャリア密度、ｎｉは真性キャリア濃度、ｅは電荷量である。例えば、Ｎｃが１０１７／ｃｍ３である場合、最大空乏層厚は０．１μｍ程度であり、キャリア密度が上昇するに伴い、空乏層厚、すなわちキャリア密度の変調が生じる領域の厚みは薄くなる。 In Equation (4), ε s is the dielectric constant of the semiconductor layer, k is the Boltzmann constant, N c is the carrier density, ni is the intrinsic carrier concentration, and e is the charge amount. For example, when N c is 10 17 / cm 3 , the maximum depletion layer thickness is about 0.1 μm, and as the carrier density increases, the depletion layer thickness, that is, the thickness of the region where the carrier density modulation occurs is thin. Become.
　一方、Ｓｉ１－ｘＧｅｘ凹凸層１３における凹凸の高さは、電気光学位相変調器１０１において、光信号電界に作用する実効的な屈折率をｎｅｆｆ、光信号の波長をλとした場合、λ／ｎｅｆｆ以下であることが好ましい。この条件を満たすことにより、光フィールドとキャリア密度変調が行われる領域との重なりが最大となり、高効率な光位相変調が実現される。 On the other hand, the height of the unevenness in the Si 1-x Ge x uneven layer 13 is determined when the effective refractive index acting on the optical signal electric field in the electro-optic phase modulator 101 is n eff and the wavelength of the optical signal is λ. , Λ / n eff or less is preferable. By satisfying this condition, the overlap between the optical field and the region where carrier density modulation is performed is maximized, and highly efficient optical phase modulation is realized.
　上記のように、Ｓｉ１－ｘＧｅｘ凹凸層１３の凹凸形状の間隔を２Ｗ以下、かつ凹凸形状の高さをλ／ｎｅｆｆ以下に設定することにより、光信号の反射が抑えられ、自由キャリアが誘電体層１２の両側で蓄積、除去、または反転する領域内に、光信号電界のピーク強度が存在する領域が重ねられるため、最も高い光変調効率が得られることとなる。 As described above, by setting the interval between the uneven shapes of the Si 1-x Ge x uneven layer 13 to 2 W or less and the height of the uneven shapes to λ / n eff or less, reflection of the optical signal can be suppressed and free. Since the region where the peak intensity of the optical signal electric field exists is superimposed on the region where carriers are accumulated, removed, or inverted on both sides of the dielectric layer 12, the highest light modulation efficiency is obtained.
　図２は、図１に示す電気光学位相変調器１０１の光伝播方向（図１に示すＺ方向）における平面図である。関連の電気光学位相変調器においては、電気信号を駆動電圧として印加した際に、比較的薄い誘電体層の両側でキャリアの蓄積、あるいは空乏化、あるいは反転が生じる。この場合、キャリア密度が変調する領域の厚みは、１００ｎｍ以下であると見積もられる。従って、光信号電界の広がりに対して、キャリア密度が変調される領域が非常に小さく、一般的に変調効率が悪いことが問題である。本実施形態の電気光学位相変調器１０１では、キャリア密度変調される領域を、ＳＩＳ接合の形状をｐドープ半導体シリコン９の表面に設けられたＳｉ１－ｘＧｅｘ層１３からなる凹凸形状の領域とすることにより、領域面積を実効的に大きくとり、光信号電界との重なりを改善し、高い変調効率を得ることができる。 FIG. 2 is a plan view of the electro-optic phase modulator 101 shown in FIG. 1 in the light propagation direction (Z direction shown in FIG. 1). In the related electro-optic phase modulator, accumulation of carriers, depletion, or inversion occurs on both sides of a relatively thin dielectric layer when an electric signal is applied as a driving voltage. In this case, the thickness of the region where the carrier density is modulated is estimated to be 100 nm or less. Therefore, the region where the carrier density is modulated with respect to the spread of the optical signal electric field is very small, and the modulation efficiency is generally poor. In the electro-optic phase modulator 101 of the present embodiment, the region where the carrier density is modulated is the uneven region formed of the Si 1-x Ge x layer 13 having the SIS junction shape provided on the surface of the p-doped semiconductor silicon 9. Thus, it is possible to effectively increase the area of the region, improve the overlap with the optical signal electric field, and obtain high modulation efficiency.
（第２実施形態）
　次いで、本発明を適用した第２実施形態に係る電気光学位相変調器１０２の断面図を図３に示す。なお、以下の第２～第５の実施形態に係る電気光学位相変調器の構成において、第１実施形態の電気光学位相変調器１０１と同一の構成には、同一の符号を付し、その説明を省略する。 (Second Embodiment)
Next, FIG. 3 shows a cross-sectional view of an electro-optic phase modulator 102 according to a second embodiment to which the present invention is applied. Note that, in the configurations of the electro-optic phase modulators according to the following second to fifth embodiments, the same components as those of the electro-optic phase modulator 101 of the first embodiment are denoted by the same reference numerals, and the description thereof will be given. Is omitted.
　電気光学位相変調器１０２では、図３に示すように、ＳＯＩ基板のｐドープ半導体シリコン９の表面において、光の伝送方向に対して直交する方向に２種類以上のＳｉ１－ｘＧｅｘ組成の積層構造１４からなる凹凸が形成されている。図３には、Ｇｅの組成ｘが異なる２種類のＳｉ１－ｘＧｅｘ凹凸層１４ａ，１４ｂからなる積層構造１４を例示している。 In the electro-optic phase modulator 102, as shown in FIG. 3, the surface of the p-doped semiconductor silicon 9 of the SOI substrate has two or more kinds of Si 1-x Ge x compositions in the direction orthogonal to the light transmission direction. Concavities and convexities made of the laminated structure 14 are formed. FIG. 3 illustrates a laminated structure 14 including two types of Si 1-x Ge x uneven layers 14a and 14b having different Ge compositions x.
　Ｇｅの組成を異ならしめた２種類以上のＳｉ１－ｘＧｅｘ凹凸層の積層構造１４が設けられることにより、Ｇｅの組成を増やした際の結晶欠陥を低減すると共に、誘電体層１２との界面付近のキャリアプラズマ効果をより高めた層構成を実現することが可能となる。 By providing the stacked structure 14 of two or more types of Si 1-x Ge x concavo-convex layers having different Ge compositions, crystal defects when the Ge composition is increased are reduced, and the dielectric layer 12 It becomes possible to realize a layer structure in which the carrier plasma effect near the interface is further enhanced.
（第３実施形態）
　次いで、本発明を適用した第３実施形態に係る電気光学位相変調器１０３の断面図を図４に示す。電気光学位相変調器１０３では、図４に示すように、ＳＯＩ層の表面に、膜厚方向に組成変調されたＳｉ１－ｘＧｅｘ凹凸層１５が形成されている。膜厚方向にＳｉ１－ｘＧｅｘの組成を変調することにより、Ｇｅの組成ｘを増やした時の結晶欠陥を低減すると共に、誘電体層１２との界面付近のキャリアプラズマ効果をさらに向上させた層構成を実現することが可能となる。 (Third embodiment)
Next, FIG. 4 shows a cross-sectional view of an electro-optic phase modulator 103 according to a third embodiment to which the present invention is applied. In the electro-optic phase modulator 103, as shown in FIG. 4, a Si 1-x Ge x concavo-convex layer 15 whose composition is modulated in the film thickness direction is formed on the surface of the SOI layer. By modulating the composition of Si 1-x Ge x in the film thickness direction, crystal defects are increased when the Ge composition x is increased, and the carrier plasma effect near the interface with the dielectric layer 12 is further improved. It is possible to realize a layer structure.
（第４実施形態）
　次いで、本発明を適用した第４実施形態に係る電気光学位相変調器１０４の断面図を図５に示す。電気光学位相変調器１０４では、図５に示すように、ＳＯＩ層の表面上のＳｉ１－ｘＧｅｘ凹凸層１６の凹凸が、光信号の伝播方向（図５に示すＺ方向）に対して、垂直な方向（図５に示すＸ方向）に形成されている。これにより、光フィールドとキャリア変調領域との重なりが改善され、より大きな変調効率が得られる。 (Fourth embodiment)
Next, FIG. 5 shows a cross-sectional view of an electro-optic phase modulator 104 according to a fourth embodiment to which the present invention is applied. In the electro-optic phase modulator 104, as shown in FIG. 5, the unevenness of the Si 1-x Ge x uneven layer 16 on the surface of the SOI layer is relative to the propagation direction of the optical signal (Z direction shown in FIG. 5). Are formed in a vertical direction (X direction shown in FIG. 5). Thereby, the overlap between the optical field and the carrier modulation region is improved, and a larger modulation efficiency is obtained.
（第５実施形態）
　次いで、本発明を適用した第５実施形態に係る電気光学位相変調器１０５の断面図を図６に示す。電気光学位相変調器１０５では、図６に示すように、ＳＯＩ層の表面上のＳｉ１－ｘＧｅｘ凹凸層１７の凹凸が、光信号の伝播方向に対して、平行な方向（図６に示すＺ方向）に形成されている。 (Fifth embodiment)
Next, FIG. 6 shows a cross-sectional view of an electro-optic phase modulator 105 according to a fifth embodiment to which the present invention is applied. In the electro-optic phase modulator 105, as shown in FIG. 6, the unevenness of the Si 1-x Ge x uneven layer 17 on the surface of the SOI layer is parallel to the propagation direction of the optical signal (see FIG. 6). (Z direction shown).
　図７は、電気光学位相変調器１０５の光伝播方向における平面図である。電気光学位相変調器１０５においても、電気光学位相変調器１０１と同様に、キャリア密度が変調される領域の厚みをＷとした場合、表面の凹凸形状の間隔は、２Ｗ以下であることが好ましい。また、Ｓｉ１－ｘＧｅｘ凹凸層１７の凹凸は、光信号の群速度を遅くするように周期的に形成されても良い。あるいは、光信号の反射を抑制するために、光信号電界に作用する実効的な屈折率をｎｅｆｆ、光信号波長をλとした時、λ／ｎｅｆｆ以下の間隔となるように非周期的に形成されても良い。このような凹凸構造により、光フィールドとキャリア変調領域との重なりがさらに改善され、より大きな変調効率を得ることが可能である。 FIG. 7 is a plan view of the electro-optic phase modulator 105 in the light propagation direction. Also in the electro-optic phase modulator 105, similarly to the electro-optic phase modulator 101, when the thickness of the region where the carrier density is modulated is W, the interval between the uneven shapes on the surface is preferably 2 W or less. Further, the unevenness of the Si 1-x Ge x uneven layer 17 may be periodically formed so as to reduce the group velocity of the optical signal. Alternatively, in order to suppress the reflection of the optical signal, when the effective refractive index acting on the optical signal electric field is n eff and the optical signal wavelength is λ, it is aperiodic so as to have an interval of λ / n eff or less. May be formed. With such a concavo-convex structure, the overlap between the optical field and the carrier modulation region is further improved, and a greater modulation efficiency can be obtained.
　次に、上記第１～第５の実施形態に係る電気光学位相変調器のキャリア変調領域の形成方法を、図８（ａ）～（ｊ）を参照しながら説明する。 Next, a method for forming the carrier modulation region of the electro-optic phase modulator according to the first to fifth embodiments will be described with reference to FIGS. 8 (a) to (j).
　図８（ａ）は、電気光学位相変調器を形成するためのＳＯＩ基板の断面図である。ＳＯＩ基板は、図８（ａ）に示すように、支持基板３上の埋め込み酸化層２に１００～１０００ｎｍ程度のｐ型ドープ多結晶シリコン９が積層された構造からなる。光損失を低減するために、埋め込み酸化層厚が１０００ｎｍ以上である構造を用いることが好ましい。埋め込み酸化層２上のｐ型ドープ多結晶シリコン９は、第１の導電タイプ（ｐタイプ）を呈するように予めドーピング処理された基板を用いるか、あるいはイオン注入などにより、ｐタイプのドーパントであるＰあるいはＢを表面層にドープ処理した後、熱処理を行っても良い。 FIG. 8A is a cross-sectional view of an SOI substrate for forming an electro-optic phase modulator. As shown in FIG. 8A, the SOI substrate has a structure in which a p-type doped polycrystalline silicon 9 of about 100 to 1000 nm is laminated on the buried oxide layer 2 on the support substrate 3. In order to reduce optical loss, it is preferable to use a structure having a buried oxide layer thickness of 1000 nm or more. The p-type doped polycrystalline silicon 9 on the buried oxide layer 2 is a p-type dopant by using a substrate previously doped so as to exhibit the first conductivity type (p-type) or by ion implantation or the like. Heat treatment may be performed after the surface layer is doped with P or B.
　次に、図８（ｂ）に示すように、ｐ型ドープ多結晶シリコン９上に、Ｓｉ１－ｘＧｅｘ層からなる凹凸を形成するための酸化膜マスク１８を低圧ＣＶＤ法などの成膜法により形成する。その後、光リソグラフィあるいは電子線リソグラフィにより光変調部に例えば幅２００ｎｍ程度の開口パターンを形成する。その後、開口パターン上に、超高真空ＣＶＤ法あるいは低圧ＣＶＤ法により、例えば高さ５０～１００ｎｍ程度のＳｉ１－ｘＧｅｘ凹凸層１３を選択成長させる。 Next, as shown in FIG. 8B, an oxide film mask 18 for forming irregularities made of a Si 1-x Ge x layer is formed on the p-type doped polycrystalline silicon 9 by a low pressure CVD method or the like. Form by the method. Thereafter, an opening pattern having a width of, for example, about 200 nm is formed in the light modulation portion by photolithography or electron beam lithography. Thereafter, the Si 1-x Ge x uneven layer 13 having a height of, for example, about 50 to 100 nm is selectively grown on the opening pattern by an ultrahigh vacuum CVD method or a low pressure CVD method.
　次に、図８（ｃ）に示すように、熱酸化プロセスにより、例えば５ｎｍ程度のＳｉＯ２からなる比較的薄い誘電体層１２を形成する。その後、ＣＶＤ法あるいはスパッタ法により、凹凸を十分被覆するように誘電体層１２上にドープされていないノンドープ多結晶シリコン１９ｎを成膜する。本工程においては、ＳＯＩ上の凹凸に起因して、ノンドープ多結晶シリコン１９ｎ上にも凹凸が転写して形成される。そして、低圧ＣＶＤ法などの成膜法により、ノンドープ多結晶シリコン１９ｎ上にＳｉＮｘからなるハードマスク層２０を形成する。 Next, as shown in FIG. 8C, a relatively thin dielectric layer 12 made of SiO 2 of about 5 nm, for example, is formed by a thermal oxidation process. Thereafter, undoped polycrystalline silicon 19n is formed on the dielectric layer 12 by CVD or sputtering so as to sufficiently cover the unevenness. In this step, the unevenness is transferred and formed also on the non-doped polycrystalline silicon 19n due to the unevenness on the SOI. Then, a hard mask layer 20 made of SiN x is formed on the non-doped polycrystalline silicon 19n by a film forming method such as a low pressure CVD method.
　次に、図８（ｄ）に示すように、光リソグラフィあるいは電子線リソグラフィによりハードマスク層２０をパターニングする。さらに、形成したパターンを用いて、光変調部において光導波路構造の幅が０．３μｍ以上２μｍ以下となるように、反応性プラズマエッチング法などにより、ノンドープ多結晶シリコン１９ｎをリブ型導波路形状に加工する。 Next, as shown in FIG. 8D, the hard mask layer 20 is patterned by photolithography or electron beam lithography. Further, by using the formed pattern, the non-doped polycrystalline silicon 19n is formed into a rib-type waveguide shape by a reactive plasma etching method or the like so that the width of the optical waveguide structure is 0.3 μm or more and 2 μm or less in the light modulation portion. Process.
　次に、図８（ｅ）に示すように、イオン注入法によりＳＯＩ層であるｐ型ドープ多結晶シリコン９上にｐ＋ドープ半導体シリコン４を形成する。 Next, as shown in FIG. 8E, a p + doped semiconductor silicon 4 is formed on the p-type doped polycrystalline silicon 9 which is an SOI layer by ion implantation.
　次に、図８（ｆ）に示すように、プラズマＣＶＤ法などの成膜法により、酸化膜クラッド層８を成膜し、ＣＭＰにより平坦化を行う。 Next, as shown in FIG. 8F, an oxide film clad layer 8 is formed by a film forming method such as a plasma CVD method, and planarized by CMP.
　次に、図８（ｇ）に示すように、上部電極引出し層となる多結晶シリコン層を積層し、ｎタイプのイオン注入により、ノンドープ多結晶シリコン１９ｎと共に、ｎタイプの導電性を示すようにドープ処理をする。また、ノンドープ多結晶シリコン１９ｎは、ｎタイプを呈するように、成膜中にドーピング処理しても良い。 Next, as shown in FIG. 8 (g), a polycrystalline silicon layer serving as an upper electrode extraction layer is stacked, and n-type conductivity is exhibited together with non-doped polycrystalline silicon 19n by n-type ion implantation. Dope treatment. Further, the non-doped polycrystalline silicon 19n may be doped during film formation so as to exhibit the n type.
　次に、図８（ｈ）に示すように、ｎドープ多結晶シリコン１０の上部電極引出し層に、イオン注入によりｎ＋ドープ多結晶シリコン１１を形成する。 Next, as shown in FIG. 8 (h), an n + doped polycrystalline silicon 11 is formed in the upper electrode lead layer of the n doped polycrystalline silicon 10 by ion implantation.
　次に、図８（ｉ）に示すように、酸化膜クラッド層８をプラズマＣＶＤ法などにより積層し、反応性エッチングによりコンタクトホール２１を形成後、ｐ＋ドープ半導体シリコン４とｎ＋ドープ多結晶シリコン１１の各表面に、電極コンタクト層６を形成する。本工程において、電極コンタクト層６は、半導体シリコン層上にＮｉなどの金属を積層して、アニールすることによりシリサイド層などで形成しても良い。 Next, as shown in FIG. 8 (i), the oxide film cladding layer 8 is stacked by plasma CVD or the like, and after forming the contact hole 21 by reactive etching, p + doped semiconductor silicon 4 and n + doped polycrystalline silicon 11 are formed. An electrode contact layer 6 is formed on each surface. In this step, the electrode contact layer 6 may be formed of a silicide layer or the like by laminating a metal such as Ni on the semiconductor silicon layer and annealing it.
　次に、図８（ｊ）に示すように、スパッタ法やＣＶＤ法によりコンタクトホール２１を埋めるようにＴｉ／ＴｉＮ／Ａｌ（Ｃｕ）あるいはＴｉ／ＴｉＮ／Ｗなどの金属層を成膜し、反応性エッチングによりパターニングすることにより、電極配線７を形成する。電極配線７の形成により、駆動回路との接続が可能になる。 Next, as shown in FIG. 8 (j), a metal layer such as Ti / TiN / Al (Cu) or Ti / TiN / W is formed to fill the contact hole 21 by sputtering or CVD, and the reaction The electrode wiring 7 is formed by patterning by reactive etching. Formation of the electrode wiring 7 enables connection with the drive circuit.
　次いで、本発明のマッハ－ツェンダー干渉計型の構造について説明する。
　図９は、本発明を適用した第６実施形態に係るＭＺＭ型光強度変調器（マッハ－ツェンダー干渉計型の構造）２０６の構成図である。ＭＺＭ型光強度変調器２０６は、上記の第１～第５の実施形態のうちのいずれかの電気光学位相変調器が平行に配置された第１のアーム２２および第２のアーム２３からなり、第１および第２のアーム２２，２３の入力側で光を分岐する光分岐構造２５と、出力側で結合する光結合構造２６が接続して設けられている。ＭＺＭ型光強度変調器２０６では、第１および第２のアーム２２，２３で光信号の位相変調が行われた後、光結合構造２６により位相干渉が行われることにより、入力光が光強度変調信号に変換される。 Next, the structure of the Mach-Zehnder interferometer type of the present invention will be described.
FIG. 9 is a configuration diagram of an MZM type optical intensity modulator (Mach-Zehnder interferometer type structure) 206 according to the sixth embodiment to which the present invention is applied. The MZM type light intensity modulator 206 includes a first arm 22 and a second arm 23 in which the electro-optic phase modulators of any of the first to fifth embodiments are arranged in parallel. An optical branching structure 25 that branches light on the input side of the first and second arms 22 and 23 and an optical coupling structure 26 that couples on the output side are connected. In the MZM type light intensity modulator 206, the phase modulation of the optical signal is performed by the first and second arms 22 and 23, and then phase interference is performed by the optical coupling structure 26, whereby the input light is modulated by the light intensity. Converted to a signal.
　ＭＺＭ型光強度変調器２０６においては、入力側に配置された光分岐構造２５により、入力光が第１および第２のアーム２２，２３に等しいパワーとなるように分岐される。ここで、第１のアーム２２に正の電圧を印加することにより、電気光学位相変調器の誘電体層の両側でキャリア蓄積が生じ、第２のアームに負の電圧を印加することにより、同誘電体層の両側のキャリアが除去されることになる。これにより、キャリア蓄積モードでは、電気光学装置における光信号電界に作用する屈折率が小さくなり、キャリア除去(空乏化)モードでは、光信号電界に作用する屈折率が大きくなり、両アームでの光信号位相差が最大となる。この両アームを伝送する光信号を出力側の光結合構造により合波することにより、光強度変調が生じることになる。 In the MZM type light intensity modulator 206, the input light is branched so as to have the same power as that of the first and second arms 22 and 23 by the light branching structure 25 arranged on the input side. Here, by applying a positive voltage to the first arm 22, carrier accumulation occurs on both sides of the dielectric layer of the electro-optic phase modulator, and by applying a negative voltage to the second arm, the same occurs. Carriers on both sides of the dielectric layer will be removed. As a result, in the carrier accumulation mode, the refractive index acting on the optical signal electric field in the electro-optical device is reduced, and in the carrier removal (depletion) mode, the refractive index acting on the optical signal electric field is increased, and the light in both arms The signal phase difference is maximized. Optical intensity modulation occurs by combining the optical signals transmitted through both arms by the optical coupling structure on the output side.
　上記構成を備えるＭＺＭ型光強度変調器２０６によれば、入力光を低電流密度、低消費電力、高い変調度、低電圧駆動、および高速変調で光強度変調することができる。 According to the MZM type light intensity modulator 206 having the above-described configuration, it is possible to modulate the light intensity of the input light with low current density, low power consumption, high modulation degree, low voltage drive, and high speed modulation.
　図１０は、本発明を適用した第７実施形態に係るＭＺＭ型光強度変調器２０７の構成図である。ＭＺＭ型光強度変調器２０７は、図１０に示すように、上記のＭＺＭ型光強度変調器２０６を並列に配置した構成を備えている。
　上記構成により、ＭＺＭ型光強度変調器２０６と同様の効果が得られると共に、入力光の光強度変調における並列処理が可能となる。 FIG. 10 is a configuration diagram of an MZM type light intensity modulator 207 according to the seventh embodiment to which the present invention is applied. As shown in FIG. 10, the MZM light intensity modulator 207 has a configuration in which the MZM light intensity modulators 206 are arranged in parallel.
With the above configuration, the same effect as that of the MZM type light intensity modulator 206 can be obtained, and parallel processing in the light intensity modulation of input light can be performed.
　図１１は、本発明を適用した第８実施形態に係るＭＺＭ型光強度変調器２０８の構成図である。ＭＺＭ型光強度変調器２０８は、図１１に示すように、複数のＭＺＭ型光強度変調器２０６、または、ＭＺＭ型光強度変調器２０７が直列に配置された構成を備えている。
　上記構成により、ＭＺＭ型光強度変調器２０７，２０８は、より高い転送レートを有する光変調器やマトリックス光スイッチなどへ応用することができる。 FIG. 11 is a configuration diagram of an MZM type light intensity modulator 208 according to the eighth embodiment to which the present invention is applied. As shown in FIG. 11, the MZM light intensity modulator 208 has a configuration in which a plurality of MZM light intensity modulators 206 or MZM light intensity modulators 207 are arranged in series.
With the above configuration, the MZM type optical intensity modulators 207 and 208 can be applied to an optical modulator having a higher transfer rate, a matrix optical switch, or the like.
　以上、本発明の好ましい実施形態について詳述したが、本発明は係る特定の実施形態に限定されるものではなく、特許請求の範囲内に記載された本発明の要旨の範囲内において、種々の変形・変更が可能である。 The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications are possible within the scope of the gist of the present invention described in the claims. Deformation / change is possible.
　以下、具体例を示す。 Specific examples are shown below.
（実施例１）
　上記の第１実施形態に係る電気光学位相変調器１０１を図８（ａ）～（ｊ）に示す工程により作製した。作製時においては、入力光の波長λを１５５０ｎｍとして、波長を勘案し、その他の条件を・・・とした。
　また、自由キャリアが誘電体層１２の両側で蓄積、除去、または反転する半導体層の厚さＷを１６０ｎｍとし、Ｓｉ１－ｘＧｅｘ凹凸層１３の凹凸の間隔をＷと同程度の１６０ｎｍ程度以下とした。 Example 1
The electro-optic phase modulator 101 according to the first embodiment is manufactured by the steps shown in FIGS. At the time of production, the wavelength λ of the input light was set to 1550 nm, the wavelength was taken into consideration, and other conditions were set as.
Further, the thickness W of the semiconductor layer in which free carriers are accumulated, removed, or inverted on both sides of the dielectric layer 12 is set to 160 nm, and the unevenness interval of the Si 1-x Ge x uneven layer 13 is approximately 160 nm, which is the same as W. It was as follows.
（比較例１）
　Ｓｉ１－ｘＧｅｘ凹凸層１３に凹凸を設けないこと以外は、実施例１と同じ条件で電気光学位相変調器を作製した。 (Comparative Example 1)
An electro-optic phase modulator was manufactured under the same conditions as in Example 1 except that the Si 1-x Ge x uneven layer 13 was not provided with unevenness.
　実施例１および比較例１で作製した電気光学位相変調器における位相シフト量の光信号伝搬方向の長さ依存を図１２に示す。キャリア変調される厚みＷと同程度の１６０ｎｍ程度以下の間隔の凹凸を形成することにより、実施例１の電気光学位相変調器における光変調効率が顕著に改善されることを確認した。Ｓｉ１－ｘＧｅｘ凹凸層１３の凹凸の深さに関しても、深さを大きくすることにより、光変調効率が改善されることを確認した。 FIG. 12 shows the dependence of the phase shift amount on the length of the optical signal propagation direction in the electro-optic phase modulator fabricated in Example 1 and Comparative Example 1. It was confirmed that the light modulation efficiency in the electro-optic phase modulator of Example 1 was remarkably improved by forming irregularities with an interval of about 160 nm or less, which is the same as the thickness W of carrier modulation. It was confirmed that the light modulation efficiency was improved by increasing the depth of the unevenness of the Si 1-x Ge x uneven layer 13.
　また、実施例１および比較例１で作製した電気光学位相変調器における動作周波数帯域のキャリア密度依存性を図１３に示す。光位相変調の動作周波数帯域は、変調効率改善によるサイズ低減の効果と凹凸を設けることによる電気容量増加の影響とトレードオフがある。基本的には、光信号電界に作用する実効的な屈折率をｎｅｆｆ、光信号波長をλとした時、凹凸の深さがλ／ｎｅｆｆ以下である場合に周波数帯域は広くなるが、キャリア密度を１０１８／ｃｍ３程度とすることにより、１０ＧＨｚ以上の高速動作が可能になることを確認した。 FIG. 13 shows the carrier density dependence of the operating frequency band in the electro-optic phase modulator manufactured in Example 1 and Comparative Example 1. The operating frequency band of optical phase modulation has a trade-off between the effect of reducing the size by improving the modulation efficiency and the effect of increasing the electric capacity by providing the unevenness. Basically, when the effective refractive index acting on the optical signal electric field is n eff and the optical signal wavelength is λ, the frequency band becomes wide when the depth of the unevenness is λ / n eff or less. It was confirmed that a high-speed operation of 10 GHz or more is possible by setting the carrier density to about 10 18 / cm 3 .
　なお、上記に加えて、周波数帯域をより改善するためには、キャリアの移動度や寿命が非常に重要である。特に、多結晶シリコン層におけるキャリアの移動度は、高速動作する上で課題として挙げられる。従って、アニール処理による再結晶化により粒子径を大きくし、キャリア移動度を改善するか、あるいはｎドープ多結晶シリコン１０に関して、エピタキシャル横方向成長（ＥＬＯ）法などを用いて結晶品質を改善することが有効である。 In addition to the above, in order to further improve the frequency band, the mobility and life of the carrier are very important. In particular, the carrier mobility in the polycrystalline silicon layer is a problem in high-speed operation. Therefore, increase the particle size by recrystallization by annealing treatment, improve carrier mobility, or improve the crystal quality of the n-doped polycrystalline silicon 10 by using an epitaxial lateral growth (ELO) method or the like. Is effective.
（実施例２）
　実施例１で作製した電気光学位相変調器を用いて、上記の第６実施形態に係るＭＺＭ型光強度変調器２０６を作製した。
　作製したＭＺＭ型光強度変調器においては、実用的な光通信システムと同程度の４０Ｇｂｐｓ以上での光強度変調、および、変調された光信号の送信が可能であることを確認した。 (Example 2)
Using the electro-optic phase modulator manufactured in Example 1, the MZM type light intensity modulator 206 according to the sixth embodiment was manufactured.
In the fabricated MZM type optical intensity modulator, it was confirmed that optical intensity modulation at 40 Gbps or higher and transmission of the modulated optical signal were possible, which was the same as that of a practical optical communication system.
　本願は、２０１２年３月３０日に、日本に出願された特願２０１２－８０４５１号に基づき優先権を主張し、その内容をここに援用する。 This application claims priority based on Japanese Patent Application No. 2012-80451 filed in Japan on March 30, 2012, the contents of which are incorporated herein by reference.
　低コスト、低電流密度、低消費電力、高い変調度、低電圧駆動、および高速変調を、サブミクロンの領域内で実現可能な、キャリアプラズマ効果に基づく光変調器構造を実現するシリコンベース電気光学装置を提供することができる。 Silicon-based electro-optics that realize an optical modulator structure based on the carrier plasma effect that can achieve low cost, low current density, low power consumption, high modulation depth, low voltage drive, and high-speed modulation in the submicron region An apparatus can be provided.
　１　　真性半導体シリコン
　２　　埋め込み酸化層
　３　　支持基板
　４　　ｐ＋ドープ半導体シリコン
　６　　コンタクト層
　６Ａ　　第１のコンタクト層
　６Ｂ　　第２のコンタクト層
　７　　電極配線
　８　　酸化膜クラッド層
　９　　ｐドープ半導体シリコン
　１０　　ｎドープ多結晶シリコン
　１１　　ｎ＋ドープ多結晶シリコン
　１２　　誘電体層
　１３　　Ｓｉ１－ｘＧｅｘ凹凸層（Ｓｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸）
　１４　　二種類以上のＳｉ１－ｘＧｅｘ組成の積層構造からなる凹凸
　１５　　組成変調されたＳｉ１－ｘＧｅｘ層からなる凹凸
　１６　　Ｓｉ１－ｘＧｅｘ凹凸層（Ｓｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸）
　１７　　Ｓｉ１－ｘＧｅｘ凹凸層（Ｓｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸）
　１８　　酸化膜マスク、
　１９　　ｎドープ多結晶シリコン、
　１９ｎ　　ノンドープ多結晶シリコン
　２０　　ＳｉＮｘハードマスク層
　２２　　第１のアーム
　２３　　第２のアーム
　２４　　電気光学装置駆動用電極パッド
　２５　　光分岐構造
　２６　　光結合構造 DESCRIPTION OF SYMBOLS 1 Intrinsic semiconductor silicon 2 Embedded oxide layer 3 Support substrate 4 p + doped semiconductor silicon 6 Contact layer 6A 1st contact layer 6B 2nd contact layer 7 Electrode wiring 8 Oxide film clad layer 9 P doped semiconductor silicon 10 n doped polycrystalline silicon 11 n + doped polycrystalline silicon 12 dielectric layer 13 Si 1-x Ge x concavo-convex layer (concavo-convex composed of Si 1-x Ge x (x = 0.01 to 0.9) layer)
14 Concavities and convexities made of a laminated structure of two or more kinds of Si 1-x Ge x compositions 15 Concavities and convexities made of composition-modulated Si 1-x Ge x layers 16 Si 1-x Ge x unevenness layers (Si 1-x Ge x ( x = 0.01-0.9) Concavity and convexity consisting of layers)
17 Si 1-x Ge x concavo-convex layer (concavo-convex composed of Si 1-x Ge x (x = 0.01 to 0.9) layer)
18 Oxide mask,
19 n-doped polycrystalline silicon,
19n non-doped polycrystalline silicon 20 SiN x hard mask layer 22 first arm 23 second arm 24 electro-optical device driving electrode pad 25 optical branching structure 26 optical coupling structure

Claims (23)

  1. 　第１の導電タイプを呈するようにドープ処理された第１のシリコン半導体層と第２の導電タイプを呈するようにドープ処理された第２のシリコン半導体層の少なくとも一部が積層された構造からなり、前記積層された第１のシリコン半導体層と第２のシリコン半導体層との界面に、比較的薄い誘電体層が形成されたＳＩＳ型接合において、前記第１および第２のシリコン半導体層に結合された電気端子からの電気信号により、自由キャリアが、前記比較的薄い誘導体層の両側で蓄積、除去、または反転することにより、光信号電界に作用する自由キャリア濃度が変調されることを利用した電気光学装置であって、
    　前記第１および第２の導電タイプを呈する第１および第２のシリコン半導体層が積層された領域において、
    　前記第１のシリコン半導体層の表面にＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が設けられており、この上に前記比較的薄い誘電体層が形成され、さらに前記第２の導電タイプを呈する第２のシリコン半導体層が積層されていることを特徴とするシリコンベース電気光学装置。     The first silicon semiconductor layer doped so as to exhibit the first conductivity type and the second silicon semiconductor layer doped so as to exhibit the second conductivity type are stacked. In a SIS type junction in which a relatively thin dielectric layer is formed at the interface between the stacked first silicon semiconductor layer and the second silicon semiconductor layer, the first silicon semiconductor layer is coupled to the first and second silicon semiconductor layers. The free carrier concentration acting on the optical signal electric field is modulated by accumulating, removing, or inverting free carriers on both sides of the relatively thin dielectric layer by the electrical signal from the electrical terminal. An electro-optic device,
    In the region where the first and second silicon semiconductor layers exhibiting the first and second conductivity types are stacked,
    The surface of the first silicon semiconductor layer is provided with irregularities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer, and the relatively thin dielectric layer is formed thereon. Further, a silicon-based electro-optical device, wherein a second silicon semiconductor layer exhibiting the second conductivity type is laminated.
  2. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、少なくとも２種類以上のＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）組成の積層構造からなることを特徴とする請求項１に記載のシリコンベース電気光学装置。 Concavities and convexities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer have at least two types of Si 1-x Ge x (x = 2. The silicon-based electro-optical device according to claim 1, wherein the silicon-based electro-optical device has a laminated structure having a composition of 0.01 to 0.9).
  3. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、Ｓｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）の組成が膜厚方向に変調された構造からなることを特徴とする請求項１に記載のシリコンベース電気光学装置。 Concavities and convexities formed of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer are Si 1−x Ge x (x = 0.01 to 0). 9. The silicon-based electro-optical device according to claim 1, wherein the composition in (9) is modulated in the film thickness direction.
  4. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、少なくとも２種類以上のＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）組成からなることを特徴とする請求項１に記載のシリコンベース電気光学装置。 Concavities and convexities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer have at least two types of Si 1-x Ge x (x = 2. The silicon-based electro-optical device according to claim 1, comprising a composition of 0.01 to 0.9).
  5. 前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、格子歪のあるＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなることを特徴とする請求項１に記載のシリコンベース電気光学装置。 Concavities and convexities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer have Si 1-x Ge x (x = 0) with lattice distortion. The silicon-based electro-optical device according to claim 1, characterized in that the silicon-based electro-optical device is composed of .01-0.9) layers.
  6. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、光信号の伝播方向に対して、垂直な方向に形成されていることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 Concavities and convexities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer are formed in a direction perpendicular to the propagation direction of the optical signal. The silicon-based electro-optical device according to claim 1, wherein the silicon-based electro-optical device is formed.
  7. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸が、光信号の伝播方向に対して、平行な方向に形成されていることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 Concavities and convexities made of a Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer are formed in a direction parallel to the propagation direction of the optical signal. The silicon-based electro-optical device according to claim 1, wherein the silicon-based electro-optical device is formed.
  8. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸の間隔が、自由キャリアが、前記比較的薄い誘電体の両側で蓄積、除去、または反転する半導体層の厚さＷに対して、２Ｗ以下であることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 The interval between the concaves and convexes made of the Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer is such that free carriers are present on both sides of the relatively thin dielectric. 6. The silicon-based electro-optical device according to claim 1, wherein the thickness is 2 W or less with respect to the thickness W of the semiconductor layer accumulated, removed, or inverted.
  9. 　前記第１のシリコン半導体層の表面に設けられたＳｉ１－ｘＧｅｘ（ｘ＝０．０１～０．９）層からなる凹凸の高さが、前記電気光学装置における光信号電界が作用される実効的な屈折率をｎｅｆｆ、光信号波長をλとした時、λ／ｎｅｆｆ以下であることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 The height of the concavo-convex formed of the Si 1-x Ge x (x = 0.01 to 0.9) layer provided on the surface of the first silicon semiconductor layer is affected by the optical signal electric field in the electro-optical device. 6. The silicon-based electro-optical device according to claim 1, wherein the effective refractive index is n eff and the optical signal wavelength is λ, which is λ / n eff or less.
  10. 　自由キャリアが、前記比較的薄い誘電体層の両側で蓄積、除去、または反転する領域内に、光信号電界がピーク強度を有する領域が配置されることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 6. A region having a peak intensity of an optical signal electric field is disposed in a region where free carriers are accumulated, removed, or inverted on both sides of the relatively thin dielectric layer. A silicon-based electro-optical device according to claim 1.
  11. 　前記第１および第２の導電タイプを呈するようにドープ処理されたシリコン半導体層が、多結晶シリコン、アモルファスシリコン、歪シリコン、単結晶シリコン、Ｓｉ１－ｘＧｅｘからなる群から選択される少なくとも一層からなることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 The silicon semiconductor layer doped to exhibit the first and second conductivity types is at least selected from the group consisting of polycrystalline silicon, amorphous silicon, strained silicon, single crystal silicon, and Si 1-x Ge x. 6. The silicon-based electro-optical device according to claim 1, comprising a single layer.
  12. 　前記第１および第２のドープ領域に形成された電気端子は、光信号損失を小さくするように、低い直列抵抗を与えながら配置されていることを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 6. The electrical terminal formed in the first and second doped regions is disposed while giving a low series resistance so as to reduce an optical signal loss. The silicon-based electro-optical device according to the item.
  13. 　光信号が伝送される領域における、前記第１の導電タイプを呈するようにドープ処理されたシリコン半導体層と第２の導電タイプを呈するようにドープ処理されたシリコン層の少なくとも一部が積層された構造が、リブあるいはリッジ型光導波路構造を呈することを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 In the region where the optical signal is transmitted, at least a part of the silicon semiconductor layer doped to exhibit the first conductivity type and the silicon layer doped to exhibit the second conductivity type are stacked. 6. The silicon-based electro-optical device according to claim 1, wherein the structure has a rib or ridge type optical waveguide structure.
  14. 　光信号が伝送される領域における、前記第１の導電タイプを呈するようにドープ処理されたシリコン半導体層と第２の導電タイプを呈するようにドープ処理されたシリコン層の少なくとも一部が積層された構造が、スラブ型光導波路構造を呈することを特徴とする請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 In the region where the optical signal is transmitted, at least a part of the silicon semiconductor layer doped to exhibit the first conductivity type and the silicon layer doped to exhibit the second conductivity type are stacked. 6. The silicon-based electro-optical device according to claim 1, wherein the structure has a slab type optical waveguide structure.
  15. 　少なくとも１つの電気変調信号が前記第１および第２の電気端子の少なくとも１つに入力として加えられ、光変調信号に変換されることを特徴とする、請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 The at least one electrical modulation signal is applied as an input to at least one of the first and second electrical terminals and converted to an optical modulation signal according to any one of claims 1-5. The silicon-based electro-optical device described.
  16. 　前記シリコンベース電気光学装置が平行に配置された第１のアームおよび第２のアームからなり、これに入力側で結合する光分岐構造と、出力側で結合する光結合構造が接続して設けられ、前記第１のアームおよび第２のアームで光信号の位相変調が行われ、前記光結合構造により位相干渉が行われることにより、光強度変調信号に変換されることを特徴とするマッハ－ツェンダー干渉計型の構造からなる、請求項１～５のいずれか一項に記載のシリコンベース電気光学装置。 The silicon-based electro-optical device includes a first arm and a second arm arranged in parallel, and an optical branching structure coupled on the input side and an optical coupling structure coupled on the output side are connected to the silicon-based electro-optical device. The Mach-Zehnder is characterized in that phase modulation of an optical signal is performed by the first arm and the second arm, and phase interference is performed by the optical coupling structure to be converted into a light intensity modulation signal. 6. The silicon-based electro-optical device according to claim 1, wherein the silicon-based electro-optical device has an interferometer type structure.
  17. 　前記第１のアームと第２のアームが非対称な構成となっている、請求項１６に記載のシリコンベース電気光学装置。 The silicon-based electro-optical device according to claim 16, wherein the first arm and the second arm have an asymmetric configuration.
  18. 　前記光分岐構造は、前記第１のアームおよび第２のアームに対して、１対１以外の入力信号分配比を与えることを特徴とする、請求項１６に記載のシリコンベース電気光学装置。 The silicon-based electro-optical device according to claim 16, wherein the optical branching structure gives an input signal distribution ratio other than 1: 1 to the first arm and the second arm.
  19. 　所定の組合せで配置された複数の別個の干渉計を備える、請求項１６に記載のマッハ－ツェンダー干渉計型の構造。 17. A Mach-Zehnder interferometer type structure according to claim 16, comprising a plurality of separate interferometers arranged in a predetermined combination.
  20. 　前記複数のマッハ－ツェンダー干渉計は、並列に配置されていることを特徴とする、請求項１９に記載のマッハ－ツェンダー干渉計の構造。 20. The structure of a Mach-Zehnder interferometer according to claim 19, wherein the plurality of Mach-Zehnder interferometers are arranged in parallel.
  21. 　前記複数のマッハ－ツェンダー干渉計は、直列に配置されていることを特徴とする、請求項１９に記載のマッハ－ツェンダー干渉計の構造。 20. The structure of a Mach-Zehnder interferometer according to claim 19, wherein the plurality of Mach-Zehnder interferometers are arranged in series.
  22. 　前記比較的薄い誘電体が、酸化シリコン、窒化シリコン、酸化ハフニウム、酸化ジルコニウム、酸化アルミニウムの少なくとも一層からなることを特徴とする請求項１～８のいずれか一項に記載のシリコンベース電気光学装置。 9. The silicon-based electro-optical device according to claim 1, wherein the relatively thin dielectric is made of at least one layer of silicon oxide, silicon nitride, hafnium oxide, zirconium oxide, and aluminum oxide. .
  23. 　前記比較的薄い誘電体の層厚が、０．１ｎｍ以上５０ｎｍ以下であることを特徴とする請求項１～８のいずれか一項に記載のシリコンベース電気光学装置。 The silicon-based electro-optical device according to any one of claims 1 to 8, wherein a layer thickness of the relatively thin dielectric is 0.1 nm or more and 50 nm or less.
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